OBSERVATIONS ON THE DEVELOPMENT OF RAIA BATIS. 39 



log 



remains permanently open. Should this prove to be a correct del rinination of the 

 parts, it will add another feature which justifies Owen, Agassi/., and others, who ha* 

 so far dissented from Cuvier as to give the Selachians a place in the zot 

 higher than that of the bony fishes. At the same time, it will git* corroborate 

 proof of the correctness of Cuvier's view, that " the rudiments of the maxillari. s, inter- 

 maxillaries, ... are evident in the skeleton."* Furthermore, we maj also assert that 

 among Selachians we have numerous instances of a double hare-lip being a normal 

 adult condition. 



Branchial Fissures and Gills. — In nearly all adult Selachians there are five gill- 

 openings in each side; Hexanchus and Heptanchus have respectively six and •eren 

 such openings. In addition to these, all of the skates and some of the sharks have a 

 peculiar opening just behind the eyes, or at some point between these and the first 

 branchial fissure, which makes a direct communication, for the most part of a large 

 size, between the top of the head and the pharynx, and to which the terms " spiracle," 

 "event," " Spritz-locher," "foramina temporalia," etc., have been applied. 



In the youngest embryos of skates here described, we have found the number of 

 gill-openings or branchial fissures seven on each side, all well defined except the last, 

 which is the smallest of the series (figs. 4 and 4 a ). These are all in 

 range from before backward, and at this stage the spiracle, as such, is not distinguished 

 from the others. It is characteristic of the early embryos of all Selachians, to have 

 developed, in connection with branchial apparatus, temporary gills, which are seen in 

 the form of long and slender filaments projecting from the sides of the neck. They 

 are generally described as coming out through the gill-openings, and as prolongations 

 of the internal gills. Cornalia,t who has made a special study of these organs, so 

 describes and figures them. We believe that, in consequence of not having seen em- 

 bryos sufficiently young, he has been led into an error. 



We have found them, when first formed, growing from the outer edge of the 



same 



branchial arch (figs. 4 a and .5), and at that time in no way connected with the bran- 

 chial fissures. In the skate, the first and seventh arch had no fringes at any period, 

 and of the five which had them, the fringes of the foremost ones were the longest, 

 the hindmost being merely short, conical projections. As development advances, the 

 bases of the fringes are gradually covered up, as it seems, by the growth of the por- 

 tion of each arch in front of them, which is thus projected outward as the body 



(N 



t 



giostomi. Memoria del Dottore Emiiio Cornalia. 1856. 



