196 F. W. GAMBLE, B.SC. 



Subfamily PromesostominjE. 



Gemis 7. — Promesostoma, v. Graff. 



Mesostomidce with two germaria and separate yolk-glands, and a common 

 genital aperture. Female accessory organs absent. Testes small. 



10. Promesostoma marmoratum (Schultze [27]). PI. X, fig. 10; 



PI. XI, fig. 16. 



Length '5 — 1 *5 mm. Body elongate, cylindrical, broadly rounded in 

 front, truncate behind. Anterior end used as a tactile organ. Colour 

 very variable. The epidermis which furnishes the ground colour is 

 colourless, bright yellow, or yellowish-red. Black reticular pigment is 

 almost constantly present as a small patch between the eyes ; elsewhere 

 to a variable extent, and may be entirely absent. The epidermis on 

 the inner side of the eyes contains immense numbers of rhabdites 

 (fifteen to twenty in a single mother cell), forming two well-defined 

 tracks. Elsewhere they are few in number. The posterior end is 

 provided with adhesive papillce. The pharynx lies just behind the 

 centre of the body. The commencement of the gut (as v. Graff 

 observed) is marked by active flagellar. 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 

 copulatory organ. The most typical form which this chitinised 

 ejaculatory duct assumes is that of a bishop's crosier, PI. XI, 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 directions 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 Mill- 

 port (v. Graff) ; Kilmore, Skye (Clapar&de) ; Port Erin, Isle of Man 

 (F, W. G.) ; Plymouth (F. W. G.). At Millport and Plymouth forms 



