4432, FRANK E. BEDDARD. 
Affinities of Genus Acanthodrilus.—I have attempted 
to show elsewhere that in one very important structural 
character—the nephridial system—the family Perichetide 
represent most nearly the ancestral Oligochet. The reproduc- 
tive organs of Perichzta are not, in my opinion, so near to 
the ancestral condition as those of Eudrilus and Teleu- 
drilus, but still they are nearer to it than those of such 
genera as Lumbricus and quite as near as those of any other 
genus at present known. As to other structural peculiarities, 
the most that can be said is that there is no reason against 
regarding Pericheta as an ancestral form. The only fact 
which it appears to me can be urged against this statement 
is the continuous circle of seta; it is perhaps usual to regard 
the paired arrangement as primitive, and the continuous circle 
of seta as derived from this; I am, however, inclined to think 
that the converse is true, and that the continuous circle 
of sete round each segment is the primitive arrange- 
ment, the paired condition secondary. 
Now, the genus Pericheta is clearly connected with 
Acanthodrilus through P. Stuartiand Deinodrilus. In 
P. Stuarti (Bourne, 14) the Perichztous organisation is 
retained, but there are two pairs of tubular atria as in 
Acanthodrilus. I have shown that Deinodrilus agrees 
with many species of Pericheta in the clitellum; it has two 
pairs of tubular atria; the sete are twelve in number in each 
segment, and are arranged in twelve longitudinal rows; their 
arrangement is in fact intermediate between that of Peri- 
cheta and that of Acanthodrilus. The nephridia of 
Deinodrilus can be explained on the hypothesis that they 
have been derived from those of Pericheta. 
Affinities of the different Species of Acanthodrilus. 
The above facts are, at least, reconcilable with the 
hypothesis that the eight sete per segment of Acantho- 
drilus have been derived by the reduction of a primitively 
greater number. Now, in most of the species of Acantho- 
drilus which have a diffuse nephridial system, the individual 
sete are, more or less, widely separated and not strictly 
