264 FRANK E. BEDDARD. 
appears to be the equivalent of a part of the spermatotheca of 
Hyperiodrilus. The genus Eudriloides which I have 
dealt with in the present paper supplies the next stage. Here 
we have a cup-shaped layer of cells which, though they have 
lost their connection with the epidermis, are very possibly to 
be regarded as a derivative of it. They do not, however, line 
the coelomic pouch, but have been, as it were, thrust aside by 
the growth of the cells lining the sac, which cells have forced 
their way to the exterior. Here, therefore, the original 
spermatotheca is entirely relieved of all share in the organ 
devoted to the storage of the sperm. Finally, Libyodrilus 
and perhaps Polytoreutus have no trace left of the original 
epidermic invagination except possibly at the very pore. I 
have shown in Libyodrilus that the sac which is formed out 
of the tissues of the septa, burrows its way into the thickness 
of the body-walls; it is quite likely that it actually reaches 
and perforates the epidermis by its own unaided efforts. The 
spermatotheca, therefore, of Heliodrilus gradually yields up 
its place to the sac developed out of the mesoblastic tissues, 
which grow as it diminishes, and finally entirely replace it. 
This instance is quite analogous, for example, to the replace- 
ment of the notochord by the vertebral column. 
§ Classification of the Eudrilide. 
This family comprises now so large a number of forms that 
it may be desirable to subdivide it. A subdivision has been 
attempted by Michaelsen (loc. cit.); but it seems to me that a 
further acquaintance with the structure of the various genera 
of the family does not tend to confirm the justice of dividing the 
family, as Michaelsen does, into two sub-families, Eudrilini and 
Teleudrilini. The diagnosis which Michaelsen gives of the 
Teleudrilini is as follows: 
“ Die Teleudrilinen sind meganephridische, mit 4 Borsten- 
paar-Reihen ausgestattete Terricolen, die eine einzige ventral- 
mediane minnliche Geschlechtséffuung auf oder am 17 
Segment und eine einzige ventral-mediane SamentaschenOff- 
nung hinter der Intersegmentalfurche 10/11 besitzen,” 
