if Division ol FishMf 



fi VJ. S. Hationa\ Wufi«« 



PROCEEDINGS 



AMERICAN ACADEMY 



ARTS AND SCIENCES. 



VOL. XIV. 

 PAPERS READ BEFORE THE ACADEMY. 



I. 



ON THE YOUNG STAGES OF BONY FISHES. 

 By Alexander Agassiz. 



Presented May 28, 1878. 



II. Development of the founders. 



A YOUNG Flounder, immediately after its escape from the egg, pre- 

 sents no special points of difference from the embryos of other bony 

 fishes, in a similar stage of growth. There are, however, in the earlier 

 stages also many points in common, to which but little attention 

 has been paid, thus far ; and the study of these characters presents, 

 from an embryological point of view, many features of special and 

 also of more general interest. As I have already treated of the de- 

 velopment of the tail and head (in Part I. of these Studies),^ the 

 gradual passage from a leptocardial tail, such as we find in PI. III. fig. 

 1, to a so-called homocercal tail (PI. IV. fig. 5), I will not refer to this 

 again, beyond calling attention to the peculiar physiognomy of these 

 young bony fishes, while in the stages (PL III. figs. 3-5, and PL IV. 

 fig. 1) during which the heterocercal tail is so prominent a feature, and 

 before the fins characteristic of the osseous fishes have become wholly 

 or partially differentiated from the primitive embryonic fin-fold, which 

 extends from the base of the head, and runs more or less parallel with 

 the dorsal chord, round the anal extremity, back toward the anterior 



* Proceedings Am. Acad. Arts and Sciences, xiii. 117. Boston, 1877. 



VOL. XIV. (n. S. VI.) 1 



