TYPHLORHYNGHUS NANUS. 647 



Typhi orliyncluis lias lost its opening to the exterior, we can 

 readily compare the female organs in this creature with those 

 of Byrsophlebs. The spermatozoa may reach the receptacu- 

 lum (funnel-shaped organ) by a duct similar to the ductus 

 longus of the latter ; such a duct would scarcely be dis- 

 cernible save in the living state and when full of sperma- 

 tozoa. 



It should be remarked that the walls of the bursa are much 

 folded, so that the lumen is quite irregular. 



(b) Male: Testes. — There is a pair of compact spherical 

 testes, one on either side of the proboscis immediately behind 

 the brain (fig. 5, Te.), each enclosed in a very delicate 

 membrane, which often is hardly distinguishable. In every 

 specimen that I have examined I have fouud apparently mature 

 spermatozoa lying for the most part on the dorsal and anterior 

 surface of either testis. The rest of the testis is composed 

 of sperm mother-cells in various stages of development. 

 I have not fouud it practicable to follow out the history of 

 the development of the spermatozoa. The appearance of 

 the cells composing the testes agrees very closely with that 

 of the germ-cells of Plagiostoma Girardi figured by von 

 Gi'aff (1. c, Taf. xvi, figs. 11 — 14). I have also compared 

 sections of the testes of Typhlorhyuchus with some of 

 Mesostomum tetragouum, 0. Sch., and find there, too, a 

 strong resemblance. Cells in a morula state are always 

 present (fig. 5, Mo.). The position of the testes is hardly 

 paralleled amongst the Mesostomidae and Proboscidas. 



In Macrorhynchus Naegelii, as figured by vou Graff 

 (loc. cit., Taf. xi, fig. 7), they extend as far forward as the 

 level of the brain and pharynx, but in no case do they lie in 

 the retractile proboscis. In most Mesostomidee and Probos- 

 cida3 the testes lie in the middle region j)f the body, and are 

 continuous with the vesiculae seminales. In Typhlorhyuchus, 

 hoAvever, I have not been able to find any communication 

 between them, although the two vesiculse always contain 

 spermatozoa in my specimens. These vesiculaa (fig. 1, V. s.) 

 are narrow tubes, with thin chitinous-looking walls, opening 



