174 



ally examined, except in a few species besides those described in this 

 paper, and it is in reality only a supposition that the structure of the 

 penial bulb is uniform in the respective species of a genus. I think, 

 however, this assumption will prove to be correct. The species within 

 each of the genera which have been examined have proved to corre- 

 spond in all particulars to such an extent that it may be safely assumed 



that the other species will also agree The copulatory cushion 



or penial bulb is of considerable importance in the classification of 

 Bnchytrcuidcu, and I have, as far as it has been possible, investigated 



its structure in all of the species described in this paper it seems 



almost certain that a great uniformity of structure exists in the differ- 

 ent species of the same genus, or in the same genera of the various 

 subfamilies. The structure of the penial bulb or corresponding organs 

 can therefore be said to be highly characteristic of both species, gen- 

 era and subfamilies." 



According to Eisen there are three distinct kinds of bulbs, the 

 mesenchytraeid bulb, the enchytrseid bulb, and the lumbricillid bulb, 

 which he defines as follows ('05, p. 7) : — 



"The Mesenchytrseid bulb is a single muscular structure, contain- 

 ing circular muscles as well as fan-shaped muscular bands connecting 

 the body wall with the periphery of the bulb. Between the muscular 

 bands are generally found numerous penial glands which open on the 

 surface of the bulb around the penial pore. The sperm-duct pene- 

 trates the bulb, opening on the center of its outer surface. 



"The Enchytrseid bulb is multiple, consisting of several separate 

 cushions grouped around the penial pore. In these cushions we find 

 several sets or fascicles of glands, each fascicle opening by itself on 

 the surface of the body. There are no muscular bands connecting the 

 base of the cushions with its periphery. The sperm-duct never pene- 

 trates the bulbs or cushions but opens close to and independently of 

 them. Exterior to the cushions there are numerous muscles connect- 

 ing the body wall immediately surrounding the pore with other parts 

 of the same somite. 



"The Lumbricillid bulb is always single and covered with a strong 

 muscular layer, which however never penetrates down between the 

 cells of the bulb. There are generally two or three distinct sets of 

 glandular cells in the bulb. Some of these open in the lower part of 

 the sperm-duct, or rather in a narrow groove in the elongation of the 

 sperm-duct. Others open on the free surface of the bulb, either ir- 

 regularly or in narrow circular fields, bunched into fascicles. The 

 sperm-duct penetrates one side of the bulb. In Bryodrilus the gland 

 which opens in the extension of the sperm-duct is covered with a thin 

 cushion of muscular strands, forming a bulb wnthin a bulb." 



