4.4.4. FRANK E. BEDDARD. 
of the setz in Oligocheta is bound up with that of the origin 
of the nephridia, though the connection between the two 
structures is not quite so close as I then thought it was. 
The connection between the three genera, Pericheta, 
Deinodrilus, and Acanthodrilus is so completely gra- 
duated that it seems impossible to avoid the conclusion that 
they represent a series of stages in the evolution of this group 
of Earthworms; and if the order of the series is as I 
have stated there is no doubt that the continuous 
sete are primitive and the paired sete secondary. 
The only alternative supposition is that Acanthodrilus is 
the more primitive form and Pericheta the last term in the 
series.! 
This position is held by Rosa (36), who bases his views upon 
certain facts in the anatomy of Acanthodrilus which seem 
to be really primitive; these are (1) the double dorsal vessel 
found in certain species, i.e. A. multiporus, (2) the presence 
in A. dissimilis of two pairs of ovaries, (3) the independence 
of the two pairs of vasa deferentia and their opening by as 
many distinct apertures, (4) the character of the nephridia of 
A. multiporus. 
The last character I need not discuss again, as I have 
already argued that Acanthodrilus, although showing affi- 
nities to the primitive form, does not come so near it as does 
Pericheta. 
With regard to No. 3, Rosa’s facts are (through no fault of 
his own) incorrect; and in any case the male reproductive 
organs of Acanthodrilus resemble those of Deinodrilus 
and Pericheta Stuarti. I have already in this paper (p. 442) 
expressed the opinion that none of these types are so near to 
the primitive condition as Eudrilus. 
(2) The presence of two pairs of ovaries is not charac- 
teristic of A. dissimilis, and it occurs occasionally in 
Lumbricus and Perionyx, and always (?) in Eudrilus. 
1 My position is of course not seriously affected by regarding Deinodrilus 
as the form from which both Acanthodrilus and Pericheta have been 
derived. 
