THE ANATOMY. PENIS 125 



a kind of penis (p), which projects into the interior of the terminal chamber. It 

 seems quite reasonable to suppose that the chamber can be everted ; in which case 

 the projection which bears the aperture of the spermiducal gland will play the part 

 of a penis. 



In all Eudrilids there is something of the same kind, but the details differ ; the 

 structures are described under the account of that family. Moniligaster at any 

 rate one species of that genus has a penis which is a little different, though it 

 agrees in being retractile. The muscular end of the spermiducal gland does not 

 open directly on to the exterior, but into a terminal chamber whose walls are 

 reflected round it ; we have, in fact, in this genus, an arrangement which is closely 

 paralleled in the Tubincidae, and not very remote from the arrangement met with in 

 Eudrilua. 



In the genera Stylodrilus, Alluroides, Stuhlmannia, Alvania, Hyperiodrilus, and 

 Sipltonogaster, there are penes of quite a different nature. In all these worms, which, 

 it will be observed, belong to three different families, the penis or penes are non- 

 retractile ; they are processes of the body -wall, which may or may not have an 

 intimate relation to the aperture of the sperm-ducts. It will be necessary to describe 

 them one by one. 



Of Stylodrilus the penis has been described by VEJDOVSKY and BENHAM. In 

 Stylodrilus gabretae the two penes are figured by the former as longish, hollow 

 processes of the body, whose walls are cellular ; they communicate directly with the 

 spermiducal glands, of which they appear to be merely a continuation, but they 

 are not retractile. 



The recently -described genus Alluroides, from East Africa, has a pair of penes 

 which are clearly outgrowths of the body-wall ; they are placed, moreover, above the 

 opening of the male-ducts ; they are peculiar in form, inasmuch as they are rather 

 thick processes, hardly tapering at the extremity, which, in the preserved examples 

 of the worm, are folded in an irregular fashion ; the organ, though not retractile, 

 seems to be probably contractile, as the shape which it assumed in the preserved 

 worms was hardly such as to ensure its usefulness as an organ for transferring 

 sperm to the spermathecae. 



The penis of Siuhlmannia has been figured, as regards its naked eye characters, 

 by MICHAELSEN (6). Its varying position is not a little remarkable ; but it always 

 lies somewhere near to the male-pore, and is at any rate connected with that pore 

 by a groove in the skin. In transverse sections of the body-wall (see Plate IV), the 

 penis is seen to be asymmetrical in structure ; it is roughly conical in outline ; one 

 side is covered by a thick glandular epithelium ; the other side is covered by an 



