180 



GUY C. ROBSON 



spermatozoon was found, viz. the ' typical '. The definitive 

 stage of the latter, which is found in the vas deferens and 

 the receptaculum seminis of the female, exhibits an 

 elongate conical ' head ', a usually well-developed acrosome, 

 an acute apical portion, no discernible middle-piece, and an 

 elongate tail. The precise length of the latter could not be 

 very satisfactorily ascertained, but it is apparently very 

 much longer than that of B y t h i n e 1 1 a, in which the tail is 

 between twice and thrice as large as the head. In P. ulvae 

 and P , taylori (Eobson MS.) the tail is relatively enormous. 

 One of the constant features of spermatogenesis is the occur- 



Text-figs. 11-12. 



Fig. 11. — Section of penis, a, free Fig. 12. — ^Trans verse section through 

 portion of ' appendage ' ; vd, vas ovarian foUicle. 



deferens. 



rence in the spermatids of an arrangement of the chromatin 

 of the nucleus in bent rods or half-hoops at the periphery of 

 the nucleus. My friend Dr. J. B. Gatenby has pointed out 

 to me the rather similar concentration of chromatin at the 

 posterior part of the nucleus in the spermatid of Murex 

 trunculus recorded by Schitz (19). I am also indebted to 

 Dr. Gatenby for pointing out to me the frequent occurrence of 

 abnormal stages of spermatocytes, though of course, as has been 

 stated above, the spermatozoa are monotypic. 



The vas deferens is thin walled during the first part of 

 its course. It passes down the columellar region and in the 

 neighbourhood of the kidney gives rise to a large glandular 

 swelling, the prostate. The latter has plicate walls in- 



