378 SYDNEY J. HTCKSON. 



when spawned. The germinal vesicle of such an ovum is 

 extremely large, its diameter being about a quarter of that of 

 the ovum, and is situated quite at its edge. In some cases a 

 large germinal spot may be found, but more frequently it is 

 absent. The vesicle contains a dense network of fibrils and a 

 considerable number of granules, which stain very deeply in 

 carmine, hsematoxylin, Loffler's blue, and other stains (fig 40). 



The protoplasm of the ovum is filled with a larger number 

 of spherical or irregular globules and granules of yolk, which 

 turn perfectly black when treated with any reagent which con- 

 tains osmic acid. 



Spermatogenesis. — The very young testis of Alcyonium 

 cannot be distinguished from the very young ovary. It con- 

 sists simply of a number of small round cells on the mesen- 

 teries covered by a layer of endoderm-cells. It soon shows a 

 difference in that the cell outlines completely disappear, and 

 the testis has then the appearance of a dense crowd of nuclei 

 (fig. 42). 



The nuclei increase immensely in numbers during the 

 summer months, but, although I have made many series of 

 sections, I have not satisfied myself of their mode of division. 

 At present I have not been able to discover any signs of 

 karyokinesis. When the testis has reached a certain size, 

 about O'l mm. in diameter, a space free from nuclei filled with 

 an irregular coagulum makes its appearance in the centre 

 (fig. 43). The coagulum shrinks somewhat in the later months 

 of the year and disappears entirely in the ripe testis, which is 

 simply filled with spermatozoa. 



The spermatozoa when mature consist of head with a cone- 

 shaped anterior end, followed by a spherical body and a long 

 flexible tail (fig. 45 a). 



On making a teased preparation of a ripe testis, a number 

 of spermatozoa may be seen bearing just behind the head a 

 clear vesicular body, similar to that described and figured by 

 Pictet (33) in Strongylocentrotus and other Invertebrates. 



The details of the formation of the ripe spermatozoon from 

 the spermatids I have not at present been able to follow. 



