CONTRIBUTIONS IO THE ANATOMY OF EARTHWORMS, 443 
paired,! and, at the same time, the buccal lobe does not divide 
the first segment, and there are dorsal pores present. In all 
these characters the species in question agree with Deino- 
drilus. I should regard these species, therefore, which are 
placed on the left side of the accompanying figure, as repre- 
senting the least modified species. A. multiporus belongs 
to this group, but is indicated in the figure as slightly 
degenerate, owing to the fact that it has lost the penial sete. 
On the right side isa branch which represents A. annectens; 
higher up, and also on the right-hand side, are a number of 
species which are rather more modified than A. annectens. 
All these, however, agree in that the nephridial system is 
reduced to a single pair in each segment. In A. annectens, 
the anterior “salivary glands” resemble those of A. multi- 
porus, and for this reason the species is placed nearer to the 
primitive stock. In all these forms the procephalic lobe does 
not divide the buccal segment. It seems to me that, from the 
nature of the procephalic lobe, the condition which characterises 
many (? all) species of Pericheta, Deinodrilus, and those 
species of Acanthodrilus which have been as yet referred to 
is the primitive one; the setz are, for the most part, separated, 
but in A. capensis they begin to be approximated, and this 
appears to be completed in A. communis. 
The remaining species I regard as the most modified ; the 
buccal lobe completely divides the buccal segment, and the 
sete are strictly paired. 
This scheme of classification of the species of Acantho- 
drilus is, of course, only tentative; the main point, how- 
ever, which I wish to bring out is, that those species 
which come nearest to Deinodrilus (i.e. which possess 
diffuse nephridia, dorsal pores, buccal lobe not dividing buccal 
segment) have scattered sete, and present, therefore, 
a stage in the evolution of strictly paired sete from 
a continuous ring. It seems to me, in fact, that, as I 
pointed out nearly five years ago, the question of the origin 
1 Tam not clear about A. scioanus. Rosa (85) does not mention the 
nephridia, but states of the sete that they are closely paired. 
