only that their range of variation is extremely wide, but that a large number of reputed genera and species have been erected upon no better foundation than that afforded by the transitory phases of types, hitherto known only in their states of more advanced development.[1]
But it would be very unreasonable to put aside these cases as so far exceptional, that no inferences founded upon them can have any application to the higher forms of animal and vegetable life. For it is only in the degree of their range of variation, that Foraminifera and Protophyta differ from Vertebrata and Phanerogamia; and the main principle which must be taken as the basis of the systematic arrangement of the former groups,—that of ascertaining the range of variation by an extensive comparison of individual forms,—is one which finds its application in every department of Natural History, and is now recognized and acted on by all the most eminent botanists and zoologists. It will be sufficient for me here to refer to the views recently advanced by Dr. J. D. Hooker, in his introduction to the Flora of Australia; the results of his extensive experience in the comparison of the Floras of different portions of the globe having led him to conclusions regarding the probable origin of the diversities they present, with which my own deductions from the study of the Foraminifera are in complete accordance. And I am authorized by Mr. T. Davidson, whose profound knowledge of the Brachiopoda enables him to speak as the highest authority upon all that relates to that most interesting group (which, like that of Foraminifera, is traceable through the entire series of fossiliferous rocks) to state that in proportion to the increase of his knowledge of its modifications of type, does he find reason to regard many of them as possessing so wide a range of variation, that he feels justified in making a large reduction in the number of specific types hitherto accounted distinct; whilst in the same proportion he finds himself able to trace with considerable probability the same specific types through a succession of geological periods,—certain Oolitic Terebratulida, for example, being the probable ancestors of existing forms; and even the Lingula of the Wenlock Silurian being specifically undistinguishable from the Lingula anatena of our present seas.
The following are the general propositions, which it appears to me justifiable to base on the researches of which I now give a résumé:—
I. The range of variation is so great among Foraminifera, as to include not merely the differential characters which systematists proceeding upon the ordinary methods have accounted specific, but also those upon which the greater part of the genera of this group have been founded, and even in some instances those of its orders.
II. The ordinary notion of species, as assemblages of individuals marked out from each other by definite characters that have been genetically transmitted from original prototypes similarly distinguished, is
- ↑ See especially on this subject the valuable researches of Dr. J. Braxton Hicks, "On the Development of the Gonidia of Lichens, in relation to the Unicellular Algæ," in Quart. Journ. of Micr. Science, October, 1860, and January, 1861.
