468 STANLEY C. BALL 



Mitoses in the process of spermatogenesis are most readily 

 observed in the younger worms; probably few spermatozoa are 

 matured after the female organs begin to function. There is 

 evidence, however, that this may happen. One series of sec- 

 tions of an old worm cut transversely shows a considerable 

 number of apparently mature spermatozoa in the posterior dorsal 

 portion of the testes and in the sperm ducts which can be traced 

 for some distance backward toward the seminal vesicle. 



The form of the spermatozoon is such as might, from its struc- 

 ture in nearly related animals, be expected. Von Graff ('02) 

 figures and describes the spermatozoon of Graffilla buccinicola 

 as 0.6 mm. in length with an oval head and a flagellum about 

 twenty-five times as long. Von Jhering ('80) found in Grafhlla 

 muricicola spermatozoa some of which exhibited bifurcated 

 heads with straight prongs. In others he was unable to ob- 

 serve this forked condition, and suggested that it might not be 

 universal. Von Bohmig describes for the same species sperma- 

 tozoa with heads thus bifurcated but with the prongs curved 

 backward. 



The spermatozoon of Paravortex gemellipara is composed 

 of an unbifurcated head 0.01 mm. in length and an extremely 

 slender cylindrical flagellum 0.10 mm. long (fig. 5). The head 

 is slightly curved at the tip. The living spermatozoa are mo- 

 tionless while in the seminal vesicle, but when liberated in sea 

 water they exhibit writhing movements. Evidently this be- 

 havior is not the normal mode of progression which takes place 

 in the atrium and antrum, for no progress is made through the 

 water; the spermatozoa merely twist about in one spot. Fre- 

 quently they remain motionless in the water. Presumably the 

 fluid inside the female passages ordinarily stimulates them 

 to action. 



The seminal vesicle in Paravortex gemellipara, as in the 

 European species of Graffilla described by the German authors, 

 functions not only as a reservoir but also as a 'ripening chamber.' 

 Beside mature spermatozoa, many spermatids are usually found. 

 Figure 48 was drawn from a living worm which had been com- 

 pressed beneath a cover slip. In this seminal vesicle there were 



