242 FIELD. [Vol. XI. 



spherical, elongates and divides into two parts, a denser ante- 

 rior and a posterior portion. The anterior forms the head, 

 the posterior the tail, which remains rolled up in the interior 

 of the cell, until the spermatozoon becomes free ; it then 

 unrolls itself. 



For many years following, the discussion was warmly waged 

 between the school of Kolliker, who regarded the spermatozoon 

 as a purely nuclear production, and those who led by Henle, 

 Schweigger-Seidel, and LaValette St. George believed that the 

 cytoplasm as well as the nucleus took part in the formation. 



LaValette St. George by a long series of brilliant work, 

 begun in 1867, made known the general course of spermato- 

 genesis, and established the nomenclature now in general use. 

 He traced the cells from the germinal epithelium, through the 

 stages called by him the spermatogone, spermatocyte and 

 spermatid to the mature spermatozoon. 



In 1 84 1 about the same time that Kolliker discovered that 

 the spermatozoa are formed from the cells of the germinal 

 epithelium, R. Wagner gave the first description of the echin- 

 oderm spermatozoon ; describing that of HolotJmria Uibulosa 

 as a "lively-motioned organism with a quite round body, and a 

 delicate tail, similar to the Samenthierchen of the teleosts." 

 Later observers confirmed this for other echinoderms: Qua- 

 trefages, 1842, for Syjiapta ijihaerens (19) ; Leydig, 1852 (16), 

 A. Baur, 1864 (i), Hamann, 1883 (10), for Synapta digitata; 

 Semper, 1868 (22), for Anapta gracilis, Chirodota iiico7igriia, 

 and HolotJmria edidis ; Koren and Danielssen, 1882 (5), for 

 Trochostoma Thompsonii; Jourdan, 1883 (14), and Vogt and 

 Jung, 1887 (23), for Holothiiria Uibulosa and Cucumaria 

 Planci. 



Practically the first investigator to give an approximately 

 complete account of the structure of the echinoderm spermato- 

 zoon was Jourdan (14). In addition to the head and tail (usu- 

 ally the only parts noticed by the earlier writers) he seems 

 from his description to have seen not only that portion, which 

 came to be called the " Nebenkern," " middle piece," " corpus- 

 cle accessoire," etc., but even that part which will in this paper 

 be shown to be the centrosome ; he says : " at the point where 



