BRITISH MARINE TURBELLARIA. 197 



with "long" and "short" copulatory organs occur; at Trieste and 

 Naples v. Graff found only forms with short ones. At Plymouth 

 most of the specimens had little or no pigment. 



Distribution. — Naples, Messina, Black Sea, Baltic, North Atlantic. 



11. Promesostoma ovoidbum (0. Schmidt, 28). 



Length '5 mm. Body oval. The dense black colour is due to 

 reticular parenchymatous pigment, which forms a thick mesh-work 

 round the internal organs. The epidermis contains large numbers of 

 rhabdites, especially developed along the inner side of the eyes, which 

 are reniform, and provided with a lens. v. Graff has observed 

 trembling movements of the eyes. I have described them as seen in 

 Pr. solea. Pharynx in the posterior third of the body. Behind it lies 

 the penis, which is pyriform, its upper part filled with spermatozoa. 

 The duct is chitinous. 



Habitat. — This species is found rarely in 5 — 15 fms. Plymouth 

 Sound (F. W. G.). 



Distribution. — Messina, Naples (v. Graff), Lesina (Schmidt), 

 Egedesminde, Greenland (Levinsen). 



12. Promesostoma solea (0. Schmidt, 32). 



Differs from the preceding species in two points, The reticular 

 pigment is less dense, and the pigment-cup of the eye sends a hooked 

 process over the outer surface of the lens, The latter point alone 

 seems to me to be constant. The amount of reticular pigment varies 

 greatly. Seen from the dorsal surface the eye has an appearance 

 similar to a miniature pan or tobacco pipe, the bowl being represented 

 by the pigment cup, and the stem or handle by the strip of pigment 

 running over the lens. The vibratory movement of the eye is 

 performed in the following way. Suppose the pan or pipe to vibrate 

 through a small angle in its plane of symmetry, in such a way that 

 the plane is horizontal, the bowl moving forwards and then backwards. 

 The actual vibrations of the eye are of this kind. Apparently one eye 

 commences, performs five or six vibrations in a second, and then stops ; 

 the other eye begins, and so on. I am not certain, however, that the 

 movements are alternate for any length of time. Of the mechanism 

 I am ignorant. 



