210 DE. W. B. BENHAM OK 



was the case in tlie specimen the " penis " of which was drawn 

 out on pealing oif the cuticle. Further investigation, as well as a 

 series of sections, shows that the penis is a cylindrical structure, 

 with strongly muscular wall, traversed by two narrow canals — the 

 sperm-duct and duct of the spermiducal gland (text-fig. 3). It 

 lies, when at rest, in the " penial sac" (text-fig. 1), and the 

 penial duct, which passes to it (6, c), is bent upon itself; when 

 in use, the free end is forced out of the male pore by the 

 contraction of the muscular wall of the sac, and the tube (c) 

 simply unbends (text-fig. 2). It is, in fact, a protrusible organ 

 and not an introvert. 



Hitherto our ideas upon the " penis " of the genus Perichceia, 

 as of other forms with stout " penial ducts," like the Acantho- 

 drilidse, have been somewhat vague ; but it has been presumed 

 that this duct is capable of eversion, i. e. it is a " pleurecbolic 

 introvert." In the present instance — as sections of the penis in 

 a condition of retraction and protrusion demonstrate — there is 

 no unfolding of the wall of the penial duct : its free end is 

 merely pushed outwards, in the same manner as the penis of 

 the Leech. 



Beddard makes the following remarks in his general account 

 of the " penis " in the Oligochseta, p. 124 of his ' Monograph.' 

 *' I have found specimens of P. Houlleti, killed in alcohol, with 

 the terminal part of the muscular duct of the spermiducal gland 

 everted. I have not noticed the occurrence of this in allied 

 forms, but it very possibly takes place." ..." In some species of 

 PerichcBta the muscular duct of the spermiducal gland opens into 

 a wide and rather thin-walled terminal chamber which opens 

 directly to the exterior : it is here, again, possible that this 

 terminal chamber is protrusible ; but I have no facts at hand to 

 prove or disprove the possibility." 



The " glandulo-muscular sac " in the present species does not 

 present the firm, compact appearance figured for the "mus- 

 cular bulb " of other species, which is usually hemispherical and 

 smooth. But the muscular tissue is loose, the fibres not being 

 so definitely arranged in circular and longitudinal series ; and 

 further, this sac contains two great oval glands, one in front 

 and the other behind the entrance of the penis (text-fig. 3, «, »'). 



Each glaqd is a somewhat pear-shaped organ lined by a single 

 layer of tall gland- cells. 



Eosa has described, in P. glandule sa, a group of conspicuous 



