126 OLIGOCHAETA 



unmodified epithelium, which is like the ordiaary epidermis. The interior of the 

 organ is occupied by a quantity of laxly-aiTanged muscular tissue. In connexion 

 with the penis there is developed a long sausage-shaped body of a nacreous aspect; 

 this gland is covered by very thick muscular walls, and is lined by not particularly 

 glandular epithelium. It narrows towards the external pore, which is situated on 

 that side of the penis which is covered by thick epidermis. The penis does not 

 always appear to be developed; I have examined a considerable number of sexually 

 mature individuals in which I could find no traces of a penis. The penis here 

 seems to be not much more than an outpushing of a part of the body -wall; the 

 muscular sac connected with it may be the equivalent of the bursa copulatrix in 

 Teleudrilus, divorced from its connexion with the rest of the terminal male efferent 

 apparatus. In the genus Hyperiodrilus there are a pair of penes, which are connected 

 by grooves with the male-pore; these penes are, as in Stuhlmannia, variable in 

 position; they sometimes lie on the same segment as that which bears the male- 

 pore, sometimes they are a segment in front, and in the latter case they are usually 

 at least asymmetrical. In my description of Hyperiodrilus I described these structures 

 as papillae ; I think that they are more comparable with the penis of Stuhlmannia, 

 with which, indeed, I compared them. There are no details as to the minute structure. 

 The penis of Siphonogaster is described under the genus. 



§ 10. Spermathecae. 



The spermathecae are very characteristic organs of the Ohgochaeta; it is only in 

 a very few forms among those whose anatomy is well known that they are absent. 

 They seem to be entirely unrepresented in the following : — 



Criodrilus lacuum. Lumbricus eiseni. 



Perichaeta acystis. AUolobophora con^tricta. 



Geoscolex maxi/nius. AUolobophora samarigera. 



Anteus gigas. Bothrioneuron vejdovskyanum. 



Siphonogaster millsoni. Bothrioneuron americanum. 



AU the remaining Oligochaeta (with possibly a few more exceptions) have a 

 varying number of pairs of these organs. Eecent researches have brought to light 

 the fact that the sperm-holding organs of the Oligochaeta are of two kinds, 

 morphologically distinct. More generally the spermathecae are sacs which are most 

 probably — though the actual origin has been traced in but few types — derivatives 

 of the epidermis. In the family Eudrilidae these spermathecae are either more or 

 less rudimentary or completely absent, their place being taken by sacs which are 

 derived from the septa of the neighbouring segments and whose cavity is thus 



