II. 



Observations on the Development 0/ Raia'batis 



By JEFFRIES WYMAN, M. D., 



HERSEY PROFESSOR OF ANATOMY IN HARVARD COLLEGE. 



Communicated January 21th, 18G4 



The following observations relate mostly to the changes which a single species of 

 skate undergoes in its outward form and structure during development. They are 

 based upon the examination of a series of eggs, collected in the spring of 1851 and 

 of the three subsequent years. The publication of them has been delayed in the 

 hope that other specimens might be obtained which would make it practicable to 

 give an account of the evolution of the internal organs. Having been disappointed 

 in this, it was thought desirable to publish such results as have already been reached, 

 believing that some of them, at least, are additions to the previous knowledge of the 

 subject. 



Egg case. — This singular structure has the general form of such parts in egg- 

 laying Selachians. The whole case, in the species here described, is between 

 and seven inches in length, of a deep greenish-brown color, and composed of minute 

 parallel filaments, which give it a striated appearance and a silky lustre. The cen- 

 tral pouch (fig. 1, a), for the protection of the yelk and the embryo, is about two 

 inches long, an inch and a half wide, bulges in the middle, and has a hollow, slender, 

 curved horn projecting from each corner. The fore end of the pouch is deeply con- 

 cave, and thickest, while the hinder is thin, nearly square, and ragged ; it is from 

 this part that the embryo escapes, after the separation of the upper and under walls 

 from each other. The hinder horns project backwards as they lie in the oviduct, 

 and are of about twice the length of those at the other end. The outer edge of 

 each horn is the more rounded, and near the free end has an oblong slit (b b') for 



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