No. I.] GAR-PIKE AND STURGEON. 53 



adduced in ontogeny. Where characters of primitive holo- 

 blastism were sought, a condition extremely meroblastic was 

 found ; and until the question of the possibility of a gain or loss 

 in food yolk should be decided, the segmenting stages of a 

 Ganoid made its ancestry appear more primitive than that of 

 existing sharks. What were the developmental conditions of 

 Cladoselachid or Pleuracanthid can never be understood, but so 

 closely did many palaeozoic sharks approach existing genera in 

 the smallest details of exoskeleton that their development 

 could with but little probability have been widely different. 

 But it would now seem evident that the Ganoid which retains 

 in the main the skeletal and exoskeletal features of the palaeo- 

 zoic types, possesses as well characters in development which 

 are suggestively elasmobranchian. And on the other hand a 

 Ganoid (Sturgeon) which has widely diverged from its palaeo- 

 zoic kindred is now found to represent a type of development 

 which is in the main to be referred to the simpler characters 

 of the more ancient Gar-pike, — but is at the same time more 

 nearly holoblastic. That total cleavage is in this case of 

 secondary nature seems a not illogical conclusion, and should 

 certainly strengthen the position of Rabl in the question of the 

 loss of food yolk. 



The study of the early development of Lepidosteus and 

 Acipenser leads to the conclusion that the ancestors of the 

 Ganoids were meroblastic, rather than holoblastic, and that 

 their kinship, as far as our present knowledge can decide, was 

 most nearly with the Elasmobranchs. 



Laboratory of the Department of Biology, 

 Columbia College, August 25, 1894. 



