156 CHIM.^.ROID FISHES AND THEIR DEVELOPMENT. 



Of the interrelationships of the various modern Chimaeroids enough has been 

 said in the foregoing pages; on many grounds it is evident that Callorhynchida 

 have retained more nearly the characters of the ancestral Holocephali than have 



Chima^rids. 



If, finally, the data of Chima^roid development be carefully scrutinized, 

 there will, I am sure, be found material for interesting reflection. For such a 

 study brings with it considerations of greater significance than the pedigree of a 

 group of little-studied vertebrates. It touches, first of all, the larger problem as to 

 the degree to which embryology may be used in determining the kinship of animals. 

 Moreover it furnishes somewhat definite illustrations of the processes— usually so 

 obscure— of "shortening up" or "concentrating" developmental stages, and of 

 embryonic "specializations." It also contributes, but in a minor degree, to the 

 problem of germinal layers and, in even a more difficult field, to the interpretation 

 of amitotic cell-division. 



