The life history of Diplodiscus temporatus Stafford. 601 



Reproductive organs. 



The testes are situated in the anterior half of the body; the 

 anterior to the right, the posterior to the left of the median plane. 

 In none of the specimens which I have examined is there a fusion 

 of the testes to form a single mass, as has been described and 

 figured by Pagenstecher (1858), Walter (1858) and Looss (1892) 

 for Amphistomum subdavatum. From each testis there comes a short 

 vas deferens the two of which join to form the common seminal 

 duct. This organ is considerably coiled. It passes anteriorly into 

 the ductus which is provided with a prostate gland. The penis 

 sheath is small and thin walled. The genital pore is situated on 

 the ventral surface just beneath the point where the two caeca join 

 together. 



The ovary is situated in the median plane, a little way behind, 

 and dorsal to, the posterior testis. It is considerably smaller than 

 one of the testes. The shell gland lies just behind the ovary. 

 A Laurer's canal runs upward and slightly forward 1o the dorsal 

 surface of the body. The uterus, which in the young adults is 

 ribbon-shaped, passes first backward from the ootype, then bends 

 forward and makes several coils before reaching the genital pore. 

 The vitellaria in this species are short in comparison to those of 

 Amphistomum subdavatum, which extend forward nearly as far as 

 the anterior ends of the main excretory trunks. In B. temperatus 

 they extend from about the level of the posterior testis backward 

 to the end of the caeca. There are from six to ten follicles in each 

 vitellarium. The anterior follicles are above, the posterior ones 

 below the level of the caecum. The vitelline duct comes otf from 

 the centre of each vitellarium at the point where it bends around 

 the inside of the caecum in its passage from the upper to the 

 lower side. 



B. Larval forms. 



1. The sporocyst. 



It has been impossible to make any observations on the deve- 

 lopment of the eggs from the adult (bisexual) generation, or the 

 infecting of the snails by the free swimming larvae. 



The youngest sporocysts found in the snails were nearlj" 

 spherical sac-like bodies about 0,1 mm in diameter. There was no 

 apparent differentiation of any axes by which one part of the body 



