what have undergone modifications due to functional changes. It is obvious that here invertebrate paleontology is in a position to answer a host of questions that could not be successfully approached by comparative anatomy of recent forms, by the direct observation of successive changes. Its methods of investigation have already been applied with wonderful success to large parts of our Paleozoic crinoids, brachiopods, bryozoans and cephalopods. And I do not doubt that the time has come when the preliminary stage of mere description of fossils is passed, and a monographic treatment of each class that would fully enter into the comparative anatomy of all structures preserved, could be profitably undertaken.
It is only by this work that paleontology can hope to make those contributions to philosophical anatomy in revealing the causes of the different structures which it is especially fitted and called upon to furnish by its ability to study the gradual development of the structures. Wherever a class of fossils has been thus thoroughly treated, it has given a fruitful crop of new hypotheses and principles, as is instanced by Hyatt's investigation of the fossil cephalopods. Most classes, and especially the corals, echinoids and trilobites, await such treatment by competent investigators.
Since physiology is that branch of biology that treats of the laws of phenomena of living organisms, it might seem hopeless to expect any information from the fossil world. This is apparently the more true in regard to the invertebrates, since a special physiology exists thus far only for men and the higher invertebrates and the recent invertebrates are largely a virgin field. For this reason also, only the most general foundations of comparative physiology have been laid, and an invertebrate fossil physiology would get as yet but little support from that side. Moreover, the main source of exact information in recent physiology is the experimental method, and this is wholly inapplicable to the fossil world.
And yet it seems to us that the empiric method upon which physiology has so long flourished promises also rich fruit in paleontology. I can do no more now than briefly mention the problems that most readily suggest themselves here. Invertebrate paleontology will be especially competent to furnish contributions to the mechanics of physiology by throwing light on the development of the means and modes of locomotion. In connection with this problem invertebrate paleontology also shows most clearly the deep-reaching influence of secondary fixation on the structure of the organism, as in the case of the strange Richthofenia among the brachiopods and the Rudistæ among the lamellibranchs. It can not fail that the progress in recent invertebrate physiology will stimulate inquiry into the physiology of the fossils; and further that, as invertebrate fossil anatomy progresses, the data for such inquiry will also come forth.
