Popular Science Monthly/Volume 27/September 1885/Recent Progress in Biology
|RECENT PROGRESS IN BIOLOGY.|
THE English universities have at various times in their history been remarkable as centers of scientific investigation and progress. The Royal Society took its origin in Oxford about two hundred and forty years ago, and from time to time there have been brilliant groups of scientific investigators in either university who have, though separated by intervals of darkness, sufficed to maintain the character of these institutions as something more than schools of classical training or mathematical gymnastic. At the present moment the energy of the Biological school, which has grown up in Cambridge within the last fifteen years, forms one of the most remarkable features among the many recent evidences of healthy life and of capacity for the performance of its great national duties which that time-honored institution has afforded.
One of the most fascinating problems of biology is that involved in the attempt to trace out the pedigrees of the immense variety of living plants and animals according to the teachings of Charles Darwin. Every animal grows from a perfectly simple homogeneous egg to the more or less complicated form which it presents when adult, and we have reason to believe that the changes through which the growing developing "embryo" passes correspond to a large extent, according to certain definite laws, with the changes through which its ancestors have passed in the greater evolution of the world. Accordingly, these embryonic changes, if rightly understood, can furnish us with the most important evidence as to the ancestry, and therewith the pedigree and family relationships, of the various kinds of existing animals. The study of embryology, from this point of view, was followed with great success by the late Professor Frank Balfour (whose early death has caused incalculable loss to science), and is being prosecuted in Germany and America, but nowhere more energetically than by Balfour's pupils. It will be readily understood that if the history of growth from the egg can furnish a clew to the ancestral relationships of various animals, then the discovery of this history in the case of curious and abnormal animals must be especially important. The histories of whole groups of common animals will necessarily be very much alike, and there is no likelihood of one differing from another in essential respects. Thus the facts with regard to the growth of birds from the egg are, in regard to large features, the same which have been carefully ascertained with regard to the common fowl. The growth from the egg of ordinary hairy quadrupeds presents the same characters as that of the rabbit, the dog, and man. The history of the changes of the eggs of fish on their way from simple homogeneity to the rich complexity of adult life is practically the same for all fish truly so called; and so we may say of insects—that one insect furnishes the history which is true of all. This, be it remembered, relates only to large and general features. But naturalists are acquainted with a number of strangely abnormal animals which will not enter into large groups and even defy classification, being neither "flesh, fowl, nor good red herring." These recalcitrant animals are not objectionable to the zoölogist; on the contrary, they are his favorites. It is these which he is most eager to study, and it is from them that he expects to obtain information which will clear up doubtful points in the scheme of relationships or pedigree which he has provisionally constructed on the basis of his acquaintance with less isolated forms. These exceptional forms of animal life are found in various parts of the world, and are often difficult of access. Nevertheless, if the naturalist is to study the growth from the egg of these animals, he must follow them to their native homes. Botanists have a great advantage over zoologists in the fact that most plants are readily transported from one locality to another, and can be cultivated in artificial climates produced in glass houses. We have at present no such skill in the treatment of animals, and accordingly the energetic Cambridge naturalists have risen to the necessities of the case. Within the last three years special journeys have been undertaken from Cambridge by members of its biological school to the uttermost parts of the earth, with the sole purpose of studying the growth from the egg of strange and interesting animals, only to be obtained in the remote regions thus visited. Mr. Caldwell, Fellow of Caius College, has gone to Australia, and is still there, for the purpose of studying the history of the growth from the egg of the duck-billed Platypus or duck-mole (Ornithorhynchus) and the spiny ant-eater (Echidna), as well as of the extraordinary lung-bearing, and therefore air-breathing, fish of Queensland known as the Barra-munda (Ceratodus Forsteri). Mr. Adam Sedgwick, Fellow of Trinity College, went in 1883 to the Cape of Good Hope expressly for the purpose of collecting live specimens and, if possible, eggs and young, of a creature very much like a caterpillar in appearance, and known as Peripatus. He obtained the most complete success, brought home to England three hundred living specimens of the extraordinary Peripatus, and has obtained from them since they have been in England young in all stages of development, which will enable him very soon to give a most valuable account of the growth from the egg of this strange form. A third member of the Cambridge school—Mr. William Bateson, of Pembroke College—has been twice across the Atlantic, in 1883 and 1884, to the coast of Maryland, U. S. A., in order to study the growth from the egg of Balanoglossus, the most important and (to the zoölogist) entertaining of all worms, since it has gill-slits like a fish and rudiments of a backbone. Mr. Bateson has made and already published (in a special supplement of the "Quarterly Journal of Microscopical Science," 1885) a complete study of the development of this worm. It is perhaps as well briefly to mention here that a "complete study" in these questions means the preparation and preservation in alcohol of hundreds of specimens of different stages of growth (often very minute) of the animal under investigation, and the subsequent cutting into series of consecutive slices, each about 1 an inch thick, of a sample of each of these stages; the scrutiny of these sections with the microscope, and the reconstruction or building up of the actual structure of the animal at each stage by a mental combination of the sections.
The expedition undertaken by Mr. Caldwell (who was aided in his equipment by funds from the Government Grant Committee of the Royal Society) is perhaps the most interesting, because the animals which he has gone to study are of large size and already more or less familial. The Ornithorhynchus and the Echidna are hairy quadrupeds (mammals) peculiar to Australasia, which differ from all other hairy quadrupeds in having, like birds, but a single aperture to the exterior for the intestine and the urino-genital canals, and in having the skeleton of the shoulder-girdle and some other features of structure similar to those of reptiles. Like those of reptiles, their bodies are comparatively cold, instead of being kept to a definite "blood-heat" (100° Fahr.) as are those of all other mammals. It had often been reported, and some kind of evidence had been given to support the statement, that these strange beasts lay their eggs like birds and reptiles, instead of retaining the egg-like structure within the body and allowing it there to develop to a certain condition of maturity as do all other hairy quadrupeds. One of Mr. Caldwell's objects was definitely to ascertain whether these animals lay eggs or not, and, of more importance than that, to examine minutely the whole history of the growth in the egg, and to compare it on the one hand with the corresponding development of birds and reptiles, on the other with that of ordinary hairy quadrupeds or mammals.
Mr. Caldwell has found out all about the eggs of these animals and collected them in quantities. The Echidna lays a single egg y which she then carries about with her in a pouch formed by a fold of skin on the ventral surface of the body, similar to the kangaroo's pouch.
The duck-mole, on the other hand, lays two eggs at a time and does not carry them about, but deposits them in her nest, an underground burrow like that of the mole. Naturalists are awaiting with great interest Mr. Caldwell's account of what goes on inside these eggs while the young one is growing there; that is to say, an account of the differences and resemblances between the structures which gradually arise in these mammals' eggs and those which are familiar to us as occurring in the case of the common fowl.
With regard to the strange fish, Ceratodus, Mr. Caldwell has been no less successful, after much disappointment and persevering search. He has lately sent home a series of photographs showing groups of the black men and women whom he employed to catch the fish, standing by the river-side and holding each one in his arms a newly captured specimen, while some twenty or thirty more of the fish are heaped on the ground. Four years ago, zoölogists were glad to buy spirit-preserved specimens of this fish in London for twenty pounds apiece. Mr. Caldwell has as yet sent home so few reports of his doings in Australia, that every one will be interested in the following letter written from New South Wales in February last: