No. 2.] THE ECHINODERM SPERMATOZOON. 243 



the tail begins there is a hyaline 'cupula,' distinctly marked 

 off from the finely granular appearing protoplasm of the head." 

 He also noticed that "after treatment with osmic acid, etc., the 

 hitherto spherical form of the head became more heart-shaped, 

 and in the interior of this, a small shining body becomes ap- 

 parent." 



Others who have more or less considered points in echino- 

 derm spermatogenesis are Selenka (21), Fol (9), Flemming (8), 

 Jensen (13), Carnoy (2), O. Hertwig (12), Hamann (10, 11), 

 Russo (20), Cuenot (3, 4). Recently Pictet (18) studied among 

 that of other invertebrates the spermatogenesis in the Echinoids. 

 But besides restricting his work to this single class, he still 

 further limited it to the manner of the change of the spermatid 

 into the spermatozoon. He showed that the head of the 

 spermatozoon is formed by the entire nucleus, and is conse- 

 quently composed of two substances, the nuclein (chromatin) 

 and the caryoplasma. Further that the nuclein was no longer 

 in separate bodies (chromosomes) but was dissolved, so to 

 speak, in the caryoplasma to form a single homogeneous mass. 

 That the tail of the spermatozoon is formed by the cytoplasm 

 of the spermatid. That the " ' corpuscle accessoire,' or * Neben- 

 kern,' is a body whose office is to eliminate from the seminal 

 cell those substances which have become useless to the sper- 

 matozoon." As to its origin he accepts the results of Platner 

 and Prenant. 



The General Mode of Echinoderm Spermatogenesis. 



The origin of the primary male sexual cells in the echino- 

 derm group agrees with that which obtains in general in the 

 other animal groups, namely, from the germinal epithelium 

 lining the inner surface of the wall of the testis. I have 

 limited my subject to the history of the germinal cells from 

 the point where, as the spermatogones, they detach themselves 

 from the germinal epithelium, until, as spermatozoa, the 

 descendants of these spermatogones penetrate into the cyto- 

 plasm of the ovum in the act of fertilization. In other words, 

 I have attempted to follow the origin and the ultimate fate of 

 the various parts which make up the spermatozoon. 



