384 Classification of Fishes 



several subclasses (by whatever name called) of true fishes: (i) 

 Some (e.g., Cuvier, J. Miiller, Owen, Lutken, Cope) arranging 

 next to the lowest the Elasmobranchiates, and, as successive 

 forms, the Ganoids and Teleosteans; (2) while others (e.g., 

 Agassiz, Dana, Dumeril, Gimther) adopt the sequence Lepto- 

 cardians, Marsipobranchiates, Teleosteans, Ganoids, and Elas- 

 mobranchiates. The source of this difference of opinion is 

 evident and results partly from metaphysical or psychological 

 considerations, and partly from those based (in the case of the 

 Ganoids) on real similarities and affinities. 



"The evidence in favor of the title of the Elasmobranchiates 

 to the 'highest' rank is based upon (i) the superior develop- 

 ment of the brain; (2) the development of the egg, and the 

 ovulation; (3) the possession of a placenta; and (4) the com- 

 plexity of the organs of generation. 



" (i) It has not been definitely stated wherein the superior 

 development of the brain consists, and as it is not evident to 

 the author, the vague claim can only be met by this simple 

 statement ; it may be added, however, that the brains compara- 

 ble in essentials and most similar as a whole to those of the 

 Marsipobranchiates are those of the sharks. In answer to the 

 statement that the sharks exhibit superior intelligence, and 

 thus confirm the indications of cerebral structure, it may be 

 replied that the impression is a subjective one, and the author 

 has not been thus influenced by his own observations of their 

 habits. Psychological manifestations, at any rate, furnish too 

 vague criteria to be available in exact taxonomy. 



" (2) If the development of the eggs, their small number, 

 and their investment in cases are arguments in favor of the 

 high rank of the Elasmobranchiates, they are also for the Mar- 

 sipobranchiates, and thus prove too much or too little for the 

 advocates of the views discussed. The variation in number of 

 progeny among true fishes (e.g., Cyprinodonts, Embiotocids) 

 also demonstrates the unreliability of those modifications 

 per se. 



" (3) The so-called placenta of some Elasmobranchiates 

 may be analogous to that of mammals, but that it is not homolo- 

 gous (i.e., homogenetic) is demonstrable from the fact that all 

 the forms intervening between them and the specialized pla- 



