DEVELOPMENT OF ACANTHODRILUS MULTIPORUS. 533 
of the nephridia are apparently at variance with the views 
which I have up to the present maintained with regard to the 
phylogenetic development of these organs in the Oligocheta. 
There can be no possibility of doubt that in Acantho- 
drilus multiporus the embryo is at first furnished with 
paired nephridia—one pair to each segment,—with the funnels 
opening into the segment in front of that in which the main 
part of the nephridium lies. This seems to indicate that 
Oligochzta with paired nephridia are in this respect more 
primitive than such forms as Acanthodrilus multiporus 
and Perichzta, where the nephridia are furnished with 
numerous irregularly arranged external pores. 
I suggested originally that the diffuse condition of the 
nephridia in the latter types was the more primitive, and that 
the paired arrangement could be derived from this by reduc- 
tion. Professor Spencer strengthened this view, though differ- 
ing from myself in certain details. Dr. W. B. Benham has 
also argued in favour of the primitive nature of the excretory 
organs in Pericheta. Others have, however, declined to 
accept this theory of the evolution of the excretory organs in the 
Oligocheta. Dr. Hisig has treated the question at great length 
in his work upon the Capitellide, naturally basing his argu- 
ments principally upon the Capitellide themselves. These 
worms were the first in which the presence of many nephridia 
in asingle segment was made known (by Dr. Hisig). Since the 
many nephridia per segment of the adult worm are preceded by 
a single pair in each segment, it appears reasonable to conclude 
that the former is the more primitive condition. 
Dr. R. 8. Bergh, who has recently contributed a series of 
valuable memoirs to the settlement of these questions, has 
nothing to say in favour of the position taken up by Spencer 
and myself. Indeed, the facts in the development of Lum- 
bricus, which he has done so much towards elucidating, 
would hardly allow him to be of our opinion. Dr. Bergh 
begs to be excused from refuting all the arguments used by 
us, for the reason that they carry their own refutation. In 
so far as concerns the longitudinal duct of Polygordius 
