Page:Popular Science Monthly Volume 77.djvu/151

Rh Another problem closely connected with that of the mode of locomotion is that of the origin of the organs of sense, and also upon this, as far as the organs of seeing at least are concerned, the fossil invertebrates are able to throw some light, as in the trilobites and eurypterids.

Another line of inquiry is that of the mode of nutrition as recognizable by the appendages, and its influence upon the general structure. Under this heading such interesting minor problems as that of the origin of parasitism arise and may be solved, as indicated by a recent publication as to the time of beginning, causes and gradual changes of parasitism, to its very complex present conditions.

Probably also the physiology of respiration will in time receive important additions as far as the echinoderms, crustaceans, scorpions and eurypterids are concerned.

The widest scope, however, will have those problems that are connected with the reactions of the organisms to their physical and chemical surroundings. The invertebrate paleontologist meets forever, in sight of the ever-changing faunules, the question, what exterior influences caused these changes? Often they can be directly recognized, as in the dwarfed faunules of the Devonic pyritiferous Tully limestone or of the bituminous Marcellus and Genesee shales or the eurypterid faunas of the Salina lagoons. The systematic investigation of these reactions through the series of formations is an inviting task.

A special problem of singular interest connected with the reaction of the organisms to the chemical surroundings is that of the composition of the shell of the invertebrates. There is good evidence for the view that the shells were at first chitinous and that but gradually they became calcareous or siliceous. This important question again is intimately connected with that of the original composition of the ocean, and this line of inquiry again leads us to the highly fascinating paleophysiological problem, lately so happily dealt with by Professor Lane, as to the geological evidence on the original composition and origin of the vital liquid, the original body temperature and the physiological origin of the hard parts of the invertebrates in general.



UR knowledge of the morphology both of the animal and plant kingdoms has been largely extended by the work of the paleontologist. Mention needs only to be made of the many species, genera and families, even orders and classes, established solely for fossil forms