BRITISH MARINE TURBELLARIA. 451 



The pharynx lies just behind the centre of the body. The 

 commencement of the gut (as v. Graff observed) is marked by 

 active flagellae. The genital aperture, provided with a 

 muscular lip, is placed behind the pharynx. Testes two, oval. 

 The connection between the two paired vasa deferentia has 

 not actually been traced. From their point of union (behind 

 the genital aperture) the single duct runs forward and expands 

 into a vesicula seminalis, which is partly filled with sperm, 

 partly with the granule-secretion. Both these products 

 are conveyed to the exterior by a very curious copula tory 

 organ. The most typical form which this chitinised ejacula- 

 tory duct assumes is that of a bishop's crosier, PI. XL, fig. 16. 

 The variations both in the number and form of the coils, and 

 also in the form of the tip of the organ (straight, curved, 

 forked), are great. The limits of variation in different direc- 

 tions would become of specific value if intermediate forms were 

 not known to occur. The germaria and yolk-glands are 

 paired and lateral. The egg-capsules are stalked. 



Habitat. — This very active littoral species has been found 

 at Millport (v. Graff); Kilmore, Skye (Claparede); Port Erin, 

 Isle of Man (F. W. G.) ; Plymouth (F. W. G.). At Millport and 

 Plymouth forms with '4ong "" 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 ovoideum (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 con- 

 tains 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. 



