EMBRYOLOGY OF CRYPTOBRANCHUS 65 



general aspects as well as along special lines is imperative ; and in 

 no other form do the embryological data promise to shed greater 

 light on phylogenetic problems than in the case of Cryptobranchus. 



For the analysis of developmental processes from a morpho- 

 geiletic point of view the eggs of Cryptobranchus present certain 

 favorable features. One of these is the presence of a larger 

 amount of yolk than is known in the egg of any other amphibian ; 

 they are thus favorable objects for the study of the influence of 

 yolk on development. The eggs, moreover, are lacking in pig- 

 ment, and the early segregation of the yolk gives a translucency 

 to parts of the embryo even in the gastrula stage, enabling one to 

 study satisfactorily in the living egg some of the internal features 

 of development. The embryo is found to respond admirably to 

 the influence of chemicals modifying the course of development; 

 for certain experiments of this sort it gives results decidedly 

 more definite than have been obtained with the embryo of the 

 frog. 



The present contribution is to be followed by other parts deal- 

 ing with the embryonic and larval development. 



This investigation has been pursued under a great variety of 

 circumstances, and with many protracted interruptions due to 

 the pressure of other work. Field work on the habits of Crypto- 

 branchus, the collection and preservation of material, and the 

 study of the living egg, have been carried on each autumn ('05- 

 '11 inclusive) in northwestern Pennsylvania. For comparison 

 with Cryptobranchus, I have collected embryological material 

 of Necturus during the seasons of 1910 and 1911, from Lake 

 Monona, Wisconsin. Laboratory work, principally on preserved 

 material, begun in the Zoological Laboratory of the University 

 of Michigan ('05-07), has been continued in the zoological 

 laboratories of Lake Forest College ('07), Syracuse University 

 ('08-09), the Bureau of Fisheries at Woods Hole (summer of 

 1908), the University of Wisconsin ('09-11), and Columbia Uni- 

 versity ('11-12). To the directors of these respective laboratories 

 I wish to express my sincere thanks for uniform courtesy in 

 placing the resources of each institution at my disposal. To 

 Professor Bashford Dean, under, whose direction the work is being 



