5l0 RiOHARD EVANS. 



on reaching the level of the antepenultimate pair of legs^ 

 leave the dorsal aspect of the animal and pass in an oblique 

 dii-ectiou towards the ventral surface. The right vas deferens 

 makes its way under tlie corresponding nerve-cord and the 

 ductus ejacuhitorius. Asa rule, the left vas deferens passes 

 under the corresponding nerve-cord, but, in some cases, it 

 does not do so. The vasa deferentia unite to form aconnnon 

 duct, the point of union being situated either on the inner or 

 on the outer side of the left nerve-cord, according as the left 

 vas deferens does or does not make its way under the cord. 

 When the point of union is on the outer side of the conl, the 

 right vas deferens passes under it so as to unite with the left. 

 After the vasa deferentia have united, they pass forwards in 

 a common sheath to the level of the antepenultimate pair of 

 legs, where the canals themselves unite. 



The common duct runs forward as far as the third pvse- 

 genital pair of legs, and there, turniug round, makes its way 

 backwards to the genital oi'ifice. When the point of nnit>n 

 of the vasa deferentia is on the outer side of the left nerve- 

 cord, the ductus ejaculatorius in passing to the genital 

 opening has to make its way under the cord; but when the 

 point of union is inside the nerve-cord, the ductus ejacula- 

 torius does not pass under it (figs. 36 and 37). 



The testes are provided with a peritoneal investment and a 

 lining of tall columnar cells, with nuclei at their base, and a 

 shai'p cell outline. The nuclei are comparatively large, 

 and the cytoplasm is clear (fig. 38). The duct which 

 passes from the testis to the seminal vesicle has the same 

 two layers as the testis, together with an intervening 

 muscular layer (fig. 39). Its lining cells are columnar 

 in form and are provided with basal nuclei, well-defined cell 

 outlines, and clear cytoplasm. The wall of the seminal 

 vesicle presents close resemblance to that of the receptaculum 

 seminis. The vas deferens at its commencement has much 

 the same appearance in section as the short duct which passes 

 from the testis to the seminal vesicle, with the difference 

 that the intermediate or muscular layer is thicker (fig. 40). 



