Studies for Students. 



THE DEVELOPMENT AND GEOLOGICAL RELATIONS 

 OF THE VERTEBRATES. 



The object of these studies is in no wise to attempt to furnish a course in verte- 

 brate palaeontology, but rather to place before the student of geology, who has no time 

 for the studv of the morphological and phylogenetic questions involved, a brief state- 

 ment of the results achieved by the workers in the more narrow field. The value of 

 vertebrate remains as indicators of the time changes in the past is so well recognized 

 that it is hoped that an orderly summary of the fossil vertebrates, with a brief indica- 

 tion of the lines along which they have developed, and references to the most helpful 

 literature, may be of value to the student, both within the limits of these articles and 

 in aiding him to extend the work by collateral reading. 



PART I. THE FISHES. 



Fishes are, in the popular language of Bashford Dean, 

 " back-boned animals, gill-breathing, cold-blooded, and provided 

 with fins." This definition may well be used if we remember 

 that the " back-bone " is not always bony, that it may be 

 entirely cartilaginous or only partly ossified. A similar condi- 

 tion may be found in all the other bones of the body and is the 

 chief reason that the early history of the fishes is hidden in the 

 deepest obscurity, for it is one of the most commonly recognized 

 facts of palaeontology, as well as one of the most deplorable, 

 that only under the most favorable conditions can the soft 

 structures of any body be preserved. From this it is easily 

 understood why the earliest remains of fishes that we possess are 

 those of forms in which the skeleton has progressed so far as to 

 be formed of solid cartilage at least, and generally of cartilage 

 with local ossification or calcification. 



The following classification of the larger groups of the fishes 



is in general use : 



393 



