146 PROCEEDINGS OF THE ACADEMY OF [March, 



individuals, and that in the sexually mature animals they are very 

 seldom seen. Evidently the present species is one of the exceptions, 

 since in fig. 1, which represents an animal with the ovaries barely 

 developed, the anastomoses are not so numerous as in a larger in- 

 dividual where the female reproductive system is fully functional. 



The brain holds a position about one-fourth the length of the animal 

 from the anterior end of the body, and after treatment with equal 

 parts of formaldehyde and glycerine may be seen with the greatest 

 distinctness to originate two extensive networks, the well-known 

 ventral one and a dorsal system which has, so far as I know, never been 

 seen in whole mounts, though it was traced with considerable accuracy 

 by Lang from a study of sections. The ventral set of nerves develops 

 from the ventral half of the brain by means of several pairs of nerves 

 which have essentially the same origin as those of P. graffii (Lang's fig. 

 4, PI. 31). These form an extensive meshwork over the entire under 

 surface of the animal, conforming in general to the plan of P. grajfii, 

 though the main fibres are more delicate and their branching is not so 

 regular. 



The dorsal system may be clearly seen with the naked eye to form 

 an extensive network over the entire dorsal surface of the body. Its 

 fibres are generally smaller than those of the ventral side and the 

 branching occurs with less frequency, thus forming meshes of larger 

 size. Three pairs of nerves give it origin, their position and mode of 

 branching being sufficiently well shown in fig. 2 to require no further 

 comment. 



In the most favorable specimen the testes are seen to be scattered 

 over the ventral surface, with the exception of the area bounded by_ 

 the two innermost longitudinal nerves. Under low magnification 

 their arrangement suggests that they and the delicate canals (vasa 

 ■efferentia) leading from them form an anastomosing system, and in 

 certain favorable situations, and especially in sections, it is possible 

 to demonstrate that such is actually the case. These minor canals 

 combine to form the vasa deferentia, which usually extend anteriorly 

 as well as posteriorly on each side from their T-shaped union with the 

 single branch extending inward to the midline, but in the present 

 species an anterior division has never been discovered. Throughout 

 its entire extent each vas deferens is a moderately convoluted canal 

 which may form a slight anastomosis at some point, as is shown in fig. 1. 



The tube resulting from the fusion of the vasa deferentia in the mid- 

 line passes at once into the small yet muscular seminal vesicle (fig. 5) 

 which is somewhat elliptical in form. From here the canal passes 



