Page:Popular Science Monthly Volume 77.djvu/149

Rh of many structures can not be elucidated, even by the embryology and comparative anatomy of the recent forms, but only by paleontology. Such a structure is, for instance, the mystifying stem of the crinoids which, by a study of the primitive ancestors of the crinoids among the cystids, is readily recognized as a dorsal evagination of the body. Likewise, to cite another example, the siphuncle of the recent Nautilus, which is obscure as a wholly rudimentary organ, is in such primitive Paleozoic cephalopods as Nanno and Piloceras, still seen in its original form and thereby recognized in its nature.

Since that which has already been accomplished in fossil anatomy is proof that there are still larger fields to be ploughed and harvested, it is proper to inquire into the best methods of this work before us.

We first need more extensive and more intensive or more detailed purely descriptive anatomical researches of the invertebrate fossils. There are many species that, when investigated in their smallest detail, are bound to give important results. I may cite here, as examples of such accomplishments, Hudson's minute study of the strange Blastoidocrinus of our Chazy rocks with its 90,000 ossicles, or that of the Eurypterus fischeri by Holm. Of this archaic fossil marine arachnoid, a relative of the scorpion and of the king crab, it can be fairly said that, as far as its chitinous integument is concerned, it is as well known as any recent species. We know, through Holm, its gills, its complex genital appendages of both sexes, and even its fine hairs and bristles. Dr. Clarke and myself have lately continued these investigations in the American eurypterids, and there observed the structure of the compound eyes, the pore system of the segments, the genital apertures, the mode of moulting, the arrangement of some of the principal muscles and other anatomical facts of interest.

It can be said that this field of detailed descriptive anatomy has been merely touched thus far, as far as our fossil invertebrates are concerned, and altogether too much neglected. This is not only true as to the gross anatomy, but still more so as to the microscopic structure. It must be conceded that owing to the secondary changes in the rocks, this latter line of investigation meets with great obstacles not fully appreciated by the zoologist, and that it is only in its infantile stage in some classes. But the results obtained by the microscopic research of the Paleozoic bryozoans in this country may be considered as a striking example of what persistency and enthusiasm may still accomplish. In microscopic anatomy of the fossils the training of a geologist is as much required as that of a zoologist and the history of these investigations shows that a zoologist without geologic training may be badly misled by the deceptive states of preservation of the fossils.

The main object of anatomical research is to result in comparative anatomy and to determine what parts are fundamental or primary and