Popular Science Monthly/Volume 32/November 1887/What American Zoologists Have Done for Evolution: 1887 Speech II
|WHAT AMERICAN ZOÖLOGISTS HAVE DONE FOR EVOLUTION.|
UNDER geographical variation many interesting facts have been added since Professor Baird, Dr. Allen, and Mr. Ridgway published their capital discoveries calling attention to the variations observed in birds and mammals coincident with their latitudinal range. William Bartram, grand-nephew of the famous botanist John Bartram, alludes to the effect of climate in modifying species. In speaking of birds he says, "The different soil and situation of the country may have contributed in some measure in forming and establishing the difference in size and qualities betwixt them."
Dr. J. A. Allen shows marked geographical variation among North American mammals in respect to size. He shows that—"1. The maximum physical development of the individual is attained when the conditions of environment are most favorable to the life of the species. 2. The largest species of a group (genus, sub-family, or family, as the case may be) are found when the group to which they severally belong reaches its highest development, or when it has what may be termed its center of distribution. 3. The most typical or most generalized representatives of a group are found also near the center of distribution, outlying forms being generally more or less aberrant or specialized." In the study of the eggs of birds of the same species. North and South, Dr. Allen shows that in the South the eggs are less in number and smaller in size. Mr. Robert Ridgway calls attention to the geographical variation observed in Dendræca.
The same author, in a discussion of a paper by Salvin in the "Transactions of the Zoölogical Society of London," on the relationships between the birds of Guadeloupe and the mainland, refers to the present genesis of species, and points to the increase in size of the bill and feet, the shorter tail and wings and darker colors, as characterizing them.
Dr. E. C. Coues, in his studies regarding geographical variation in color among North American insectivorous mammals, says: "My studies up to the present go to show a very interesting parallelism with the state of the case I have determined for other small mammals, notably the mice and gophers, and which my friend Mr. Allen has admirably brought out in his studies of the squirrels. In some cases I find almost identical effects of climatic or other conditions upon the shrews and the mice of particular localities, by which they both acquire the same facies loci. Present indications are that the normal variability of the shrews in size, shape, and color is not less than has been determined to hold good in various other families of mammals." In this memoir Dr. Coues has verified a curious fact, first pointed out by Professor Baird, of the modifications of the premolar dentition which the Western species collectively, as compared with the Eastern, have undergone: "A striking peculiarity of all the Western species, no matter how diverse in other respects, is to have the 'third premolar' decidedly smaller than the 'fourth,' while in all the species east of the Rocky Mountains (with one possible exception) the same tooth is as large as, or larger than, the other. Of the fact there is no question; it may be observed in an instant, and is unmistakable. Its significance is another thing. Some of the Western species are scarcely distinguishable if at all from their respective Eastern analogues, except by this character, and they all show it."
Professor A. Hyatt finds in sponges geographical variation in color, referring to similar features in birds as recorded by Baird and others.
Professor David S. Jordan, in a paper on the distribution of freshwater fishes, presents a concise series of propositions which govern these animals in the United States. They all point to the action and importance of physical conditions as governing distribution. Space will permit only the quoting of the last proposition, which is a summing up of his conclusions: "The distribution of fresh-water fishes is dependent on (a) fresh-water communication; on (b) character of stream, that is, of water, as to purity, depth, rapidity, vegetable growth, etc.; on (c) the character of the river-bed, as to size, condition of bottom, etc.; on (d) climate, as determined by latitude and by elevation above the sea; and, finally, on (e) various unknown factors arising from the nature or the past history of the species in question, or from the geological history of the rivers."
Dr. James Lewis has observed a not unlike condition of things in the distribution of the fresh-water mussels of Ohio and Alabama. By a series of tables he calls attention to what he believes is the occurrence of identical and equivalent species in the two systems of drainage, and suggests that, owing to the number of varieties characterizing the Unionidæ they may be identical. This author has also studied the genus Io and its habits, and notices its variation coincident with latitude and temperature.
Dr. R. E. C. Stearns, in a paper on the circumpolar distribution of certain fresh-water mussels and the identity of certain species, unites many hitherto recognized species of Anodonta. Dr. J. G. Cooper, in a study of the fossil and sub-fossil land-shells of the United States, sees the strongest evidence in support of the idea that the older ones are the direct ancestors of certain forms living to-day.
Mr. R. P. Whitfield read a paper before the Boston Society of Natural History, showing changes produced in Limnæa megasoma "when kept in an aquarium. Having at the outset three specimens, two of them finally died, and from the remaining one eggs were produced, presumably unimpregnated. These eggs hatched, and from these the next year came a second generation, which in turn produced a third generation the following year. The animal of Limnæa is hermaphrodite. Nevertheless, besides diminished size in the shell, it was observed that the male parts had disappeared, and the liver had become considerably reduced in size. He shows that a diœcious species had in a short time become monœcious as a result of the new physical conditions of life in the constricted quarters of an aquarium.
An instructive paper by D. W. D. Hartman, on the genus Partula of the Hawaiian Islands, shows in the most convincing manner the effect of environment in modifying the species. He finds a common occurrence of hybrids among certain forms, the result of the union of proximate species. This hybridization occurring even between arboreal and ground species. Dr. Hartman states that "gravid females are often washed by heavy rains from a favored position to drier levels, where after a few generations the progeny become depauperated, and so stunted in size as to be mistaken for distinct species." Dr. W. H. Dall, in some general considerations regarding the environment of the deep-sea mollusks, as compared with the shallow water and littoral forms, shows how much the littoral forms have to contend with in the struggle for existence as compared with the deep sea forms, and the delicate sculpture and extreme fragility of many of the shells occurring in the deeper abysses of the sea are to be explained on the ground of their habitat. Dr. Carl F. Gissler has presented some interesting evidences of the effect of chemico-physical influences in the evolution of the branchiopod crustaceans.
The effect of mechanical strains as producing like morphological effects has been treated in a masterly way by Dr. John A. Ryder. He cites the vertebral axes of turtles and extinct armadillos, also the sacra of birds and mammals, and says: "These observed coincidences, it is believed, are neither accidental, nor designed by an active cause external to these organisms or their cosmic environment. I would rather believe that the structures, so far as they have been evolved in parallel or similar ways, are the results of like forces conditioning growth and nutrition in definite modes and determinate directions. The manner of incidence of the modifying forces being in all cases determined by the voluntary actions of the organisms, the actions in turn are determined by the degree of intelligence of the animal manifesting them."
In considering the "Laws of Digital Reduction," Dr. Ryder gives a concise presentation of the various groups of animals, showing in each the line of mechanical strain in the extremities and its correlation with the increased development of those digits bearing this strain, and the consequent reduction or atrophy of those digits out of this line. These considerations led him to the following conclusions:
"1. That the mechanical force used in locomotion during the struggle for existence has determined the digits which are now performing the pedal function in such groups as have undergone digital reduction.
"2. That where the distribution of mechanical strains has been alike upon all the digits of the manus or pes, or both, they have remained in a state of approximate uniformity of development.
"3. It is held that these views are Lamarckian and not Darwinian—that is, that they more especially take cognizance of mechanical force as a mutating factor in evolution, in accordance with the doctrine of the correlation of forces."
Dr. Ryder further says, "It seems a most convincing proof of the doctrine of descent to find man an instance of the same kind of specialization determined by the manner of the distribution of strains as is so often found among the lower groups, such as the horses, sloths, jumping-mice, and even-toed ungulates."
In another memoir Dr. Ryder considers the mechanical motion in forming and modifying teeth. Considering first the simplest form of movement in the mammal's jaw, opening and closing, without fore and aft or lateral movement, he shows the successive changes going on coincident with the more complex movements of the jaw, and that the enamel foldings, ridges, crests, etc., have apparently been modified in conformity with the ways in which the force used in mastication was exerted.
Professor A. Hyatt, in an exhaustive study of the Planorbis of Steinheim, shows among other things the effect of gravitation as accounting for the form of the mollusk-shell, citing examples from all the classes, and even drawing examples from other subkingdoms to support his views.
Professor E. D. Cope, in a memoir on "Archæsthetism," considers the hypothesis of use and effort, the office of consciousness, etc. He attempts to show that consciousness is primitive and a cause of evolution. He sustains his thesis by a series of arguments which, if not beyond my grasp, would be too extensive to present here. I can only repeat the regret I expressed in the Buffalo address, namely, that neither Professor Cope nor Professor Hyatt has yet been induced to present to the public an illustrated and simple outline of their theories. Such a demonstration, I am sure, would be acceptable not only to the public but to many scientific students as well. While these two eminent naturalists believe fully in the derivative theory, they insist that Darwin's theory is inadequate to explain many of the phenomena and facts which they encounter in their studies. Darwin has distinctly said in his first edition of the "Origin of Species," "I am convinced that natural selection has been the main but not the exclusive means of modification"; and in his sixth edition of the same work, in quoting these words, he laments that he is still misunderstood on this point. The theory of acceleration and retardation of these authors is, if I understand it rightly, a very plain case of natural selection. It was inevitable that those individuals that matured the quickest were better prepared to defend themselves, were quicker in the field, were able to give their offspring an earlier start in the season, were in every way more fitted to survive than those which matured later. It is assumed that this is a law, when, to my mind, it seems the simplest result of natural selection. Instead of overriding it, it is only a conspicuous result and proof of it.
A parallel case may be seen in the increase in size of the brain in the vertebrates, and conspicuously in the higher vertebrates, since their first appearance in geological history. The individual brain clearly varies in size, and it does not require a great effort to perceive how in the long run the greater brain survives in the complex struggle for existence. Associated with the greater development, parts that were freely used for locomotion before are now compelled to perform additional service, and through the law of use and effort, which all admit as an important factor, organs are modified in structure, the anterior portion of the body assumes a new aspect; and it was on the character of these parts and aspects that Professor Dana was led to formulate his comprehensive and ingenious principle of cephalization. It is a result and not a cause. And so I believe, though with great deference to Cope and Hyatt, that the laws of acceleration and retardation, exact parallelisms, inexact parallelisms, and still more inexact parallelisms, and many other laws and theories advanced by these gentlemen, are not causes but effects, to be explained by the doctrine of natural selection and survival of the fittest.
The connecting links and intermediate forms which the skeptical public so hungrily demand are continually being discovered. Great gaps are being closed up rapidly; but the records of this work, being published in the journals of our scientific societies, are hidden from the public eye as much as if they had been published in Coptic. So rapidly have these missing links been established that the general zoologist finds it difficult to keep up with the progress made in this direction. He can hardly realize the completion of so many branches of the genealogical tree.
Professor Cope, who has accomplished so much in this direction, says; "Those who have, during the last ten years, devoted themselves to this study, have been rewarded by the discovery of the course of development of many lines of animals, so that it is now possible to show the kind of changes in structure which have resulted in the species of animals with which we are familiar as living on the surface of the earth at the present time. Not that this continent has given us the parentage of all forms of animal life, or all forms of animals with skeletons, or vertebrae, but it has given us many of them. To take the vertebrata, we have obtained the long-since extinct ancestor of the very lowest vertebrates. Then we have discovered the ancestor of the true fishes. We have the ancestor of all the reptiles, of the birds, and of the mammals. If we consider the mammals, or milk-givers, separately, we have traced up a great many lines to their points of departure from very primitive things. Thus we have obtained the genealogical trees of the deer, the camels, the musk, the horse, the tapir, and the rhinoceros, of the cats and dogs, of the lemurs and monkeys, and have important evidence as to the origin of man."
In 1874 he predicted that the ancestor of all the mammals would be a five-toed, flat-footed walker, with tubecular molar teeth, or in exact language, a pentadactyl, plantigrade bunodont. Seven years after, he obtained evidences that such a type of mammals abounded in North America during the early Eocene Tertiary period. Professor Cope, in his phylogeny of the camels, shows a remarkable parallel to that of the horse, both forms appearing in the Lower Eocene. Mr. Eugene N. S. Ringueberg believes he has found in a thin layer of limestone at Gasport, New York, a deposit in which a number of forms of brachiopods seem to present the intermediate stages between certain brachiopods common to the Clinton and the group of rocks immediately above. While the majority of species in this deposit belong to the Niagara, there are among the fossils met with three species of brachiopods which were supposed to have passed out of existence with the Clinton. He finds in this bed thirty-two forms peculiar to the Niagara, eleven common to Niagara and Clinton, three belonging to the Clinton, and two characteristic forms of the transition group. Many of these show intermediate characters.
Professor II. S. Williams, in his paleontological studies of the life history of Spirifer lævis, in which he traces the ancestral line of this creature, says: Whatever theoretical description we may give to species, here are, in the first place, an abundance of individual organisms whose remains are found in the Upper Silurian rocks of Europe, Great Britain, and America, presenting a few clearly marked, distinctive characters, which are found variously developed in the individual forms, but so grading in the various varieties as to cause careful naturalists to associate them as varieties of a single species."
Dr. C. A. White, in his comparisons of the fresh-water mussels and associated mollusks of the Mesozoic and Cenozoic periods with living species, expresses his belief that the present Unios of North America, particularly those forms allied to Unio clavus, have come down in an unbroken line from the Jurassic and possibly from earlier times. He shows that thus far all the fossil Unios have been obtained from lacustrine deposits, none of these beds being distinctly fluviatile. He furthermore calls attention to the fact that "these lacustrine formations are of very great extent in Western North America, and, without doubt, the lakes in which they were deposited were caused by encircling bands of rising land during the elevation of the continent. These great landlocked waters were at first brackish, but finally became, and for a long time remained, fresh, continuing so until their final desiccation." From this commingling of salt and fresh water he justly assumes that many modifications arose in the forms of Unios subjected to these influences, and hence has resulted a variety of forms which have gone on continually widening to the present day.
Professor A. G. Wetherby, in a paper on the geographical distribution of certain fresh-water mollusca and the possible cause of their variation, shows the paucity of forms of Unionidæ on the Pacific and Atlantic coasts as compared to the richness and profusion of those forms in the central portion of the continents. He remarks also on the absence of the family Strepotomidæ, east of the Alleghanies. He assumes that the first fresh-water forms were lacustrine. He points out the well-known geological fact of large inland inclosures and their subsequent drainage, and shows the vicissitudes which must have been encountered by species in the variety of physical conditions implied by these changes. In this connection I may be permitted to call attention to the fact that at a meeting of this Association, at Hartford, in 1874, I made a communication on the origin of the North American Unionidæ, in which I urged some of the points made by Dr. White and Professor Wetherby.
Dr. Thomas H. Streets, in studying the immature plumage of the North American shrikes, was much struck with the close resemblance between the plumage of the young of Sula cyanops and the adult plumage of another species. Recalling a generalization made by Darwin, that "when the young differs in color from the adult, and the colors of the former are not, as far as we can see, of any special service, they may generally be attributed, like various embryological structures, to the retention by the young of the characters of an early progenitor." He then shows the gradation between the several species of shrikes from this standpoint, and traces their descent from a common ancestor.
Professor S. A. Forbes, in a study of the "Blind Cave Fish and their Allies," is led to review the conclusions reached by Professor F. W. Putnam in his interesting papers on the subject. Professor Putnam brought forth a number of arguments which seemed to him to militate against the views urged by evolutionists that their peculiar characters were adaptive and the result of their cave-life. He was led to the conclusion that the absence of light had not brought about the atrophy of the eyes, the development of special sense-organs, and the bleaching of the skin. In referring to another cave-fish, Chologaster, with eyes fully developed, it was urged that the argument in regard to eyeless fishes could have no weight. In response to this it was answered that possibly Chologaster had not been subjected to subterranean influences long enough to be affected, and this objection was anticipated by urging that we have no right to assume that Chologaster is a more recent inhabitant of the caves, until proved.
The discovery of another species of Chologaster, taken from a spring at the base of a limestone cliff in Illinois, has given Professor Forbes an opportunity to make careful comparisons with the cave Chologaster. He says in regard to it, "The most important and interesting peculiarity of this species indicates a more advanced stage of adaptation to a subterranean life than that of its congeners." Referring to Professor Putnam's arguments. Professor Forbes says that "the discovery of a species of Chologaster, which frequents external waters, of an immediate subterranean origin, supplies all needed proof that the genus either has a shorter subterranean history than Amblyopsis, or, at any rate, has remained less closely confined to subterranean situations; and that in either case the occurrence of eyes, partial absence of sensory papillæ and persistence in color, are thus accounted for consistently with the doctrine of 'descent with modification.'" In this connection it may be of interest to read the curious fact recorded by Mr. S. H. Trowbridge, of the discovery in the Missouri River of a shovel-nosed sturgeon which had the skin growing over the eyes, completely inclosing them. Dr. S. H. Scudder, in a memoir read before the National Academy, brings forward evidence to show that ordinal features among insects were not differentiated in Palæozoic times, but that "all Palæozoic insects belonged to a single order which, enlarging its scope as outlined by Goldenberg, we may call Palæo-dictyoptera; in other words, the palæozoic insect was a generalized hexapod, or more particularly a generalized Heterometabolon." In a memoir on the earliest winged insects of America, embracing a reexamination of "The Devonian Insects of New Brunswick," published by the author. Dr. Scudder replies to some sharp criticisms and objections made by Dr. Hagen, and pertinently says, that "there is no evidence—but the contrary—that Dr. Hagen in his investigations uses the 'theory of descent' as a working hypothesis, without which no one studying any group of animals in the period of its rise and most rapid evolution can expect to do otherwise than stumble and wander astray. To refuse it is to merit failure."
Professor J. S. Kingsley, in his study of Limulus, regards it as an Arachnid, but states that its ancestors take us back to a time when the distinctions between the Crustacea and Arachnida were far less marked than now.
Dr. A. S. Packard, in a paper on the "Genealogy of the Insects," shows by means of a "genealogical tree" the descent of the class from the Thysanura, with some hypothetical creature not unlike Scolopendrella, as the probable stem-form of the hexapods. It is through the resemblance the larvæ of the different orders of insects bear to various members of the Thysanura that this scheme is justified. It may not be out of place to say here that the use of the "genealogical tree," in suggesting the probable line of descent of various allied groups, has been severely condemned by some as leading to no practical good in classification. It seems to me, however, the only clear scheme for the proper working out of the ascertained or hypothetical relationsliips of animals; it is thought-exciting, its very attitude provokes studious inquiry and suggestive inferences. It may be called the modern tree of knowledge.
The modern genealogical tree as used by the biological student (and as well by the ethnologist, philologist, and others) is a graphic diagram of the relationships between groups as understood by the projector, and, as such, is a most commendable and useful method with which to illustrate his meaning. With additional knowledge one can see at a glance the points that need strengthening, and he can pare, prune, or even graft new fruits on the old stock, or, if it is rotten at the trunk, cut it down altogether. These trees have always been in vogue with the older naturalists, only, in the old style of arboriculture, the trunk was always kept stiffly vertical, while the branches were bent down and trained horizontally, being flimsily attached to the main stem by printers' devices of long and short brackets. In this attitude it reminded one of the dwarfed and deformed trees of the Chinese, and very properly typified the dwarfed and deformed way of looking at classification.
Never was the provisional use of a genealogical tree more completely justified than m a memoir by Dr. Alexander Agassiz on the "Connection between Cretaceous and Echinid Faunæ." He certainly speaks in uncertain terms when, in considering the Spatangoids of the chalk, he says, "They lead us directly through the Palæostominæ and the Collyritidæ to the Ananchytidæ which have persisted to the present day," and other relationships of the same nature are repeatedly urged as would not only justify the use of the genealogical diagram against which be so strongly inveighed in his admirable address before this Association at the Boston meeting; but had he adopted this method, a much clearer view of the very points he wished to emphasize would have been afforded his readers.
It was the strictures of Agassiz above referred to that led Professor W. K. Brooks to write a paper on the subject of "Speculative Zoölogy," in which he most earnestly and ably defends the use of genealogical diagrams, and justly says: "If phylogenetic speculations retard science, speculations upon homology must do the same thing; and the only way to avoid danger will be to stick to facts, and, stripping our science of all that renders it worthy of thinking men, to become mere observing machines."
Since 1876 Professor Marsh and Professor Cope have in various journals and Government publications presented the results of their discoveries of the past vertebrate life of North America. The General Government has published the two great monographs of Professor Marsh on the Dinocerata, an extinct order of gigantic mammals, and the Odontornithes, an order of extinct toothed birds, as well as Professor Cope's great volume on the Tertiary Vertebrata, besides other memoirs by the same authors. Space will forbid more than a passing allusion to the varied and remarkable additions to our knowledge of extinct vertebrate life made by these naturalists.
Had a moiety of the work accomplished by these investigators been known to Geoffroy Saint-Hilaire, the theory of descent would have been established long before Darwin, though to Darwin and Wallace belongs the full credit of defining the true cause. Leidy, Marsh, and Cope have not only brought to light a great number of curious beasts, many of them of gigantic and unique proportions, but forms revealing in their structure the solution of many morphological puzzles, and throwing light on the derivation of many obscure parts.
The discovery in the Western tertiaries of multitudes of huge and monstrous mammals and, earlier still, of gigantic and equally monstrous reptiles, naturally led at once to an inquiry as to the cause of their extinction, "Nothing can be more astonishing," says Professor Joseph Le Conte, "than the abundance, variety, and prodigious size of reptiles in America up to the very close of the Cretaceous, and the complete absence of all the grander and more characteristic forms in the lowest Tertiary; unless, indeed, it be the correlative fact of the complete absence of mammals in the Cretaceous, and their appearance in great numbers and variety in the lowest Tertiary. . . . The wave of reptilian evolution had just risen to its crest, and perhaps was ready to break, when it was met and overwhelmed by the rising wave of mammalian evolution." In this paper of Le Conte's, which is entitled "On Critical Periods in the History of the Earth and their Relation to Evolution: and on the Quaternary as such a Period," may be found an excellent rejoinder of Professor Clarence King's lecture before the Sheffield Scientific School on the subject of "Catastrophism and Evolution."
Among the most interesting discoveries connected with these creatures is the determination by Professor Marsh that these early mammals, birds, and reptiles had brains of diminutive proportions. He says in regard to the order Dinocerata, a group of gigantic mammals whose remains have been found in the tertiary deposits of the Rocky Mountain region, that they are the most remarkable of the many remarkable forms brought to light. The brain of these creatures was remarkable for its diminutive proportion. So small, indeed, was the brain of Dinoceras mirabile, that it could "apparently have been drawn through the neural canal of all the presacral vertebræ." In alluding to the successive disappearance of the large brutes, the cause is not difficult to find: "The small brain, highly specialized characters, and huge bulk, render them incapable of adapting themselves to new conditions, and a change of surroundings brought extinction. The existing proboscidians must soon disappear, for similar reasons. Smaller mammals, with larger brains, and more plastic structure, readily adapt themselves to their environment, and survive, or even send off new and vigorous lines. The Dinocerata, with their very diminutive brain, fixed characters, and massive frames, flourished as long as the conditions were especially favorable; but, with the first geological change, they perished, and left no descendants." Professor Marsh says that the brain of Dinoceras was in fact the most reptilian brain in any known mammal.
Professor Cope, in describing the brain of Coryphodon from the deposits of New Mexico, says: "The large size of the middle brain and olfactory lobes gives the brain as much the appearance of that of a lizard as of a mammal." This is one of the lowest mammalian brains known. There are others from the Lower Eocene with equally low brains as Arctocyon of Gervais and Uintatherium of Marsh. Cope believes that the type of brain of these early creatures is so distinct as to necessitate the erection of a third sub-class of equal rank with the groups Gyrencephala and Lycencephala, which he would define as the Protencephala. He shows their approximation to reptiles.
Cope refers to Gratiolet as showing that a great development of the olfactory is a character of an inferior type; in fact, the more we ascend into paleontological antiquity, the more we find that the olfactory lobes display a greater development in comparison with the cerebral hemispheres. Dr. B. G. Wilder has shown that in the lamprey the only part which can be regarded as a cerebral hemisphere lies laterad of the olfactory lobe. In Dipnoi he finds that the cerebral outgrowth is ventrad. In another paper he says: "In either of these directions in which what may be regarded as the special organ of the mind is projected among these low or generalized forms, there would seem to be mechanical obstacles to any considerable expansion; but dorsally there is opportunity for comparatively unlimited extension, and it is in this direction that the hemispheres begin to develop in the Amphibia and attain such enormous growth in birds and mammals." How far the small brain and presumably stolid intellects brought about the extinction of the huge tertiary mammals may be better understood by the suggestions offered by Professor A. E. Verrill in a lecture at Yale College, entitled "Facts Illustrative of the Darwinian Theory." He shows what an important factor parental instinct is in the evolution of species. He regards the lack of parental care "as one of the probable causes, though usually overlooked, of the extinction of many of the large and powerful reptiles of the Mesozoic age and of the large mammals of the Tertiary." He says: "The very small size of the brain and its low organization in these early animals are now well known, and we are justified in believing that their intelligence or sagacity was correspondingly low. They were doubtless stupid and sluggish in their habits, but probably had great powers of active and passive resistance against correspondingly stupid carnivorous species. But unless the helpless young were protected by their parents, they would quickly have been destroyed; and such species might, in this way, have been rapidly exterminated whenever they came in contact with new forms of carnivorous animals, having the instinct to destroy the new-born young of mammals, and the eggs and young of oviparous reptiles. Thus it would have come about that the more intelligent forms, by the development of the parental instinct for the active protection of their young against their enemies, would have survived longest, and therefore would have transmitted this instinct, with other correlated cerebral developments, to their descendants."
Professor John Fiske, in his "Cosmic Philosophy," arrived at a similar conclusion in regard to early man. He showed that, when variations in intelligence became more important than variations in physical structure, then they were seized upon, to the relative exclusion of the latter.
The derivative theory has not only clearly revealed the fact that animals have been derived from pre-existing forms, but it shows even more clearly that organs have been evolved as well. It is difficult, in a general review of this nature, to separate clearly the two classes of facts.
Professor Cope has traced the genesis of the quadritubercular tooth in the mammals of the present day. He finds that the type of the superior molar tooth of the mammals of the Puerco epoch was triangular or tritubercular—that is, with two external and one internal tubercle. Of forty-one species of mammals of this epoch all but four of them had this type of tooth. He finds that this tooth exists to-day only in the insectivorous and carnivorous marsupials. In brief, he shows a gradual change taking place from the early primitive type of tooth in the gradual development of another tubercle. The same author, in defining the characters of an ancient order of mammals, the Amblypoda, says they are the most generalized order of hoofed mammals, being intermediate in the structure of their limbs and feet between the Proboscidia, the Perissodactyla, and Artiodactyla, which fact, together with the small size of the brain, places them in antecedent relation to the latter, in a systematic sense, connecting them with the lower mammals with small and smooth brains still in existence; and in a phylogenetic sense, since they precede the other orders in time, they stand in the relation of ancestors.
Professor Cope, in a paper read before this Association on the "Classification of the Ungulata," gives special attention to the arrangement and character of the carpal and tarsal bones. He shows that "the weaker structure of the carpus and tarsus appears first in time; that the stronger structure appeared first in the posterior limbs, and that the interlocking structure has greatly multiplied, while the linear has dwindled and mostly disappeared. Here is a direct connection between mechanical excellence and survival."
In the light of Mr. Caldwell's unquestionable determination of the oviparous character of that curious mammal, the duck-bill mole, associated with its known reptilian bearings as deduced from its skeleton and other features, the deductions of Professor Cope regarding the "Relations between the Theromorphus Reptiles and the Monotreme Mammalia" are of great interest.
In the Theromorpha are two divisions, one of which, the Pelycosauria, is limited to the Permian, and of one of this group he makes the following comparisons: "1. The relations and number of the bones of the posterior foot are those of the Mammalia much more than those of the Reptilia. 2. The relations of the astragalus and calcaneum to each other are as in the Monotreme Platypus anatinus. 3. The articulation of the fibula with both calcaneum and astragalus is as in the Monotreme order of mammals." In brief, he shows the affinity of this reptile to be with the monotremes, and that the affinities are very important in the light of Mr. Caldwell's researches, and the further fact that the development of the egg is meroblastic confirms, so to speak, the reptilian affinities of the monotremes.
Here, then, are a series of observations by different observers from different standpoints, all telling the same story. Osteologists have long ago pointed out the reptilian affinities of the monotremes from the character of the skeleton. The anatomists in like manner have insisted upon certain reptilian characters as well as avian characters from its internal structure. A trained zoölogist now studies it on the ground, and finds it laying true eggs, a fact that had been insisted upon several times in the present century. More significant still, the study of these eggs shows that they go through a reptilian mode of development. And now the paleontologist brings to light the remains of a reptile from the Permian rocks, and again establishes the same relations.
In this connection the examination by Dr. Henry C. Chapman of a fetal kangaroo and its membranes is of interest. The fœtus he examined was fourteen days old. He states that it had no true placenta, and says, "If the parts in question have been truthfully described and correctly interpreted, as partly bridging over the gap between the placental and non-placental vertebrates, they supply exactly what the theory of evolution demands, and furnish, therefore, one more proof of the truth of that doctrine."
- Address of the retiring President of the American Association for the Advancement of Science, delivered at the New York meeting, August 10, 1887.
- "Bulletin of the United States Geological Survey of the Territories."
- "Bulletin of the Nuttall Ornithological Club," vol. i, p. 74.
- Ibid., p. 81.
- Ibid., vol. ii, p. 58.
- "Bulletin of the United States Geological Survey of the Territories," vol. iii. No. 3, p. 635.
- "Memoirs of the British Society of Natural History," vol. ii, part iv.
- "American Naturalist," vol. xi, p. 607.
- "Proceedings of the Philadelphia Academy of Natural Sciences," 1877, p. 26.
- "American Naturalist," vol. x, p. 321.
- "Proceedings of the California Academy of Natural Sciences."
- Ibid., Tol. i, No. 4, p. 235.
- "American Naturalist," vol. xiv, p. 51.
- Ibid., vol. xvi, p. 581.
- "Bulletin of the Museum of Comparative Zoölogy," vol. xii, No. 6, p. 183.
- "Proceedings of the American Associated Antiquarian Society," vol. xxix, p. 657.
- "American Naturalist," vol. xii, p. 157.
- Ibid., vol. xi, p. 603.
- "Proceedings of the Philadelphia Academy of Natural Sciences," 1878, p. 45.
- "American Naturalist," vol. xvi, p. 441. Also "Proceedings of the American Associated Antiquarian Society," vol. xxix, p. 527.
- "American Naturalist," vol. xvi, p. 454.
- "Popular Science Monthly," vol. xxvii, p. 605.
- "American Naturalist," vol. xx, p. 611.
- Ibid., vol. xvi, p. 711.
- "American Journal of Science and Arts," vol. xx, p. 456.
- "Bulletin of the United States Geological Survey of the Territories," vol. iii, No. 3.
- "Journal of the Cincinnati Society of Natural History," vol. iii, p. 357, and vol. iv, p. 156.
- The following is a brief abstract which was published in the Hartford "Courant," August, 1874: "Mr. Morse, in explaining the origin of the North American Unionidæ, did not pretend to point out the absolute line of descent in these forms, but wished to call attention to some curious features in the possible derivation of the fresh-water families of mollusks from cognate genera living in salt water. It is observed, first, that the few families of fresh-water mollusks are intimately related to those forms which live in the sea between high and low water mark, and those which can withstand the influence of brackish water. He cited certain families of fresh-water mollusks which are so closely related to tidal forms as hardly to be distinguished from them. . . . In explaining the immense number of species of fresh-water mussels in America compared to the very few forms in Europe, we might look to an explanation of this feature in the past geological history of the two continents.
"In Europe there have been no great inland seas, while in America its past history shows the inclosing of large tracts of water in which freshening from brackish water went on, and, while many forms succumbed to these changed conditions, only those forms survived which resemble certain littoral species. And with the curious modifications that must have taken place in these changed conditions, one gets a possible explanation of the great variety of mollusks in our Western rivers."
- "American Naturalist," vol. xvii, p. 389.
- "American Naturalist," vol. xvi, p. 1.
- "Science," vol. iii, p. 587.
- "American Naturalist," vol. xix, p. 877.
- "American Naturalist," vol. xvii, p. 932.
- "American Journal of Science and Arts," vol. xxiii, p. 40.
- "Popular Science Monthly,' vol. xxii, pp. 195, 364.
- "American Journal of Science and Arts," vol. xiv, p. 99.
- "American Journal of Science and Arts," vol. xxix, p. 173.
- "American Naturalist," vol. xv, p. 312.
- "National Academy of Sciences," 1876.
- "American Journal of Science and Arts."
- "American Naturalist," vol. xxi, p. 546.
- "Science," vol. i, p. 303.
- "American Naturalist," vol. xvii, p. 407.
- Wheeler's "United States Geographical Survey," vol. iv, part ii, p. 182.
- "Proceedings of the American Associated Antiquarian Society," vol. xxxi, p. 477.
- Ibid., vol. xxxiii, p. 471.
- "Proceedings of the Philadelphia Academy of Natural Sciences," 1881, p. 468.