BRITISH MARINE TURBELLARIA. 205 



Testes lie at the sides of the pharynx. The vasa deferentia unite in a 

 sperm-vesicle, close to which is the granule vesicle. The long muscular 

 cylindrical penis receives both secretions, and is enclosed in an inner 

 chitinous sheath and an outer muscular one. The armature is in the 

 form of hooks with rounded basal ends. The hooks vary in size and 

 shape, and are disposed as in v. Graff's pi. x, fig. 17, of his 'Mono- 

 graphic' The genital aperture is surrounded by numerous glands. 

 The germaria lie at the sides of the penis. The reticular yolk-glands 

 are of considerable extent. 



Habitat. — In tide-pools, and among Fucus and Laminaria below 

 the surface of the sea. Kilmore, Skye (Claparede) ; Millport (v. 

 Graff) ; Plymouth ; Port Erin, Isle of Man (F. W. G.). 



Distribution. — Bergen (Jensen), Heligoland (Metschnikoff). 



The well-developed musculature of these forms enables them to 

 resist compression without rupture. If a mature individual be treated 

 in this way the various parts of the genital apparatus stand out with 

 diagrammatic clearness. 



This species, closely similar to the next in external appearance, can 

 be distinguished by the presence of the common muscular envelope 

 round the vesiculse seminales and granulorum. 



Genus 13. — Maororhtnchus, v. Graff. 

 Acrorhynchinos with a common genital aperture, two germaria, and paired 

 elongate testes. Vesicidce seminales and granulorum distinct, the duct 

 of the latter with a special chitinous tube ('Monogr.,' p. 321). 



Von Graff divides this genus into two subdivisions: — i. Typici. — Those 

 in which a poison-dart (Gift-Stachel) is absent ; duct of the vesicula 

 seminalis without chitinous armature, ii. — Venenosi. — Those provided 

 with a poison-dart ; a chitinous investment for both the duct of the 

 seminal and granule-vesicles. 



i. Typici, 



22. Maororhtnchus Naegelii (Kolliker, 17). PI. X, fig. 5 ; 



PI. XI, fig. 15. 



Length 2-2 mm. in my largest specimens ; v. Graff states that he 

 has not seen larger ones at Millport, while Mediterranean examples 



