ON THE STEUCTUEE OF VEEMICULUS PILOSUS. 259 



and although much convoluted, appears to be continuous 

 throughout. Here and there this canal enlarges into an 

 ampulla, in which waves a flame-like bunch of cilia pointing 

 towards the external aperture (figs. 28, 31, and 32, c. a.). 

 No cilia are found anywhere else but in these 

 ampullae, which are not very numerous. 



The gonads consist of a pair of testes on the anterior wall 

 of the 10th segment (fig. 12, t.), and a pair of ovaries on the 

 anterior wall of the 11th segment (fig. 12, ov.). The sperm- 

 ducts are rather short tubes opening by means of widely 

 opened shallow ciliated funnels into the 10th segment (fig. 12, 

 sp.f.). A short narrow duct passes from behind the funnel 

 through the 11th septum, rapidly changes into a thick tube for 

 about half its course, then narrows again and opens into a 

 median chamber below the nerve-cord (fig. 12, sp. ch.). 

 This cavity, which may be called the median spermiducal 

 chamber, opens to the exterior towards the posterior end of 

 the 11th segment (fig. 2, m. p. sp.) by an irregular longitu- 

 dinal aperture. The openings of the sperm-ducts into the 

 chamber are situated very near together, close to the nerve- 

 cord (fig. 22, sp. p.) 



Fig. 24 represents a median longitudinal section through 

 the spermiducal chamber; it shows how the nerve- cord [n. c.) 

 and the ventral blood-vessel {v. v.) pass over it. From the 

 structure of its wall with the cuticle, the epidermal cells [ep.), 

 the longitudinal and circular muscle-fibres (c. m. and I. m.), 

 the median chamber is obviously a direct invagination of the 

 body-wall. Moreover, that this is really the case is proved 

 by the fact that in the young worm the sperm-ducts 

 come separately to the surface (fig. 23, sp.), and there 

 is then no sign of a median pore. The gradual formation of 

 the median chamber can be traced from its earliest beginning. 



The sperm-duct, except the narrow terminal region, is 

 ciliated. The structure of the wide region is shown in a 

 longitudinal section in fig. 17, where it is seen that its large 

 size is chiefly due to the covering of coelomic epithelium cells 

 (c. ep.), which have become modified into long columnar cells 



