ENCHYTR^ID^ 1 7 



the various kinds of glands constitutes most excellent species char- 

 acteristics. 



Petiial bulb. — As ' penial bulb ' I designate the large muscular 

 cushion which in the vast majority of species, surrounds the lower 

 part of the sperm-ducts. This penial bulb differs in structure from 

 the corresponding organ in all the other genera of this family, so far 

 as they are known to me. In Mesenchytrceus the penial bulb is made 

 up of a large number of muscular strands, both longitudinal and 

 transverse. Between these strands are situated the penial glands. In 

 the penial bulbs of the other genera there exist no such muscular 

 strands, the bulb consisting simply of a large number of unicellular 

 glands situated close together and surrounded by a thin muscular 

 covering, there being no muscles inside the bulb. This structure of 

 the penial bulb is so characteristic that I have added it to the defini- 

 tion of the genus. In no single instance is a penial bulb of the 

 construction so common in Mesenchytrceus found in any other 

 genus, and similarly in Afesenchytrcetis no bulb of a structure sim- 

 ilar to that of Lumbricillus and J^ridericia^ etc., has ever been 

 observed. 



On the other hand, it is true that in some species of Mesen- 

 cJiytrceus we meet with a greatly degenerated penial bulb. Thus, 

 for instance, in M. fontinalis and in M. pedatus the penial 

 bulb is so diminished that it may be said to be virtually absent, 

 its place having been taken by a few penial glands surrounding the 

 pore. 



In M, orcce and AI. kincaidi the bulbs are small and not furnished 

 with any glands, but their muscular structure is distinct. 



Spermatophores . — In my original definition of the genus Mesen- 

 chytrceus (Eisen '79) I mentioned the presence of sperm -balls. Since 

 that time no similar structures have been observed in any Enchytraeid 

 species until now. As will be described more in detail, spermatophores 

 are actually present in several species and are especially prominent in 

 M. franciscanus. The spermatophores are found free in the ccelomic 

 cavity after having been fully developed in the sperm-sacs. In the 

 species described in this paper the spermatophores are never found in 

 the sperm-funnels or in the spermathecae. This, however, does not 

 exclude the possibility that in other species they may be found to occur 

 in such organs. 



