144 THE POPULAR SCIENCE MONTHLY 
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 compar- 
ative 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 struc- 
tures. Wherever a class of fossils has been thus thoroughly treated, it 
has given a fruitful crop of new hypotheses and principles, as is in- 
stanced 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 inverte- 
brate fossil physiology would get as yet but little support from that 
side. Moreover, the main source of exact information in recent physi- 
ology 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 physi- 
ology 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 Rudiste 
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. 
