1912. S NATURAL SCIENCES OF PHILADELPHIA. 469 



lost to sight owing to the opacity of the animal, but as they appear 

 here and there in sections it is probable that the network spreads 

 over the entire dorsal surface of the body. The average size of the 

 component nerve bundles is less than those of the ventral side, and 

 the mesh work is considerably more open; otherwise there are no 

 especially noteworthy features not represented in the figures. 



Heath ('07) has described a dorsal nervous system, conforming 

 to the same general plan, in Planocera hawaiiensis, and it is known 

 to exist in the trematodes (cf. Heath '02). Lang has theoretically 

 related the ctenophores and the flatworms on the basis of several 

 deep-seated resemblances, appearing especially in the course of the 

 embryological development. In the ctenophores there is, as is well 

 known, a nervous system fashioned on the quadriradial plan. In 

 the chiton larva there are likewise indications that in the early stages 

 the central nervous system is constructed upon essentially the .same 

 plan. In the chiton the dorsal limbs of the cross-shaped fundament 

 disappear apparently without becoming functional, but it is possible, 

 though by no means proven conclusively, that they persist in the 

 polyclads and develop into the network of the dorsal side of the body. 



The testes, ventral as usual, are united by delicate sperm capilla- 

 ries with the convoluted but unbranched vasa deferentia (PL XII, 

 fig. 4), which present the form of an inverted-U-shaped loop. The 

 outer limb of each loop passes backward to fuse with its mate imme- 

 diately behind the female reproductive pore. The inner trunk 

 extends inward and backward and unites with its fellow in the mid 

 line to form a short common duct (PL XVI, fig. 30), which at once 

 enters the posterior end of the large, elliptical seminal vesicle situated 

 close behind the pharynx. Leaving the seminal vesicle anteriorly, 

 the sperm canal, functioning as a ductus ejaculatorius, turns direct ly 

 backward and, piercing longitudinally the very large, oval granular 

 gland, immediately enters the base of the penis. This last-named 

 organ in this species is unusually long and attenuate, and is con- 

 tained in a similarly slender sheathing chamber at whose apex the 

 external pore is located. 



The ovaries are dorsal and are united by tubes, very indistinct 

 except during the egg-laying season, that in turn connect with the 

 uteri. These last-mentioned canals meet across the mid line ante- 

 riorly (PL XII, fig. 4) not far from the posterior border of the brain 

 and, arc-like, extend backward with occasional anastomoses in some 

 individuals, if not in all. In some cases well-deVeloped outpouchings 

 of the uteri occur, especially in the region of the brain and at a point 



