272 
PRANK E. BEDDARD. 
The Evolution of the Excretory Organs in Earth- 
worms. 
I shall now proceed to deduce, from the facts described in 
the present paper and in Professor Spencer’s account of 
Megascol ides, what I believe to have been the course of 
development of the nephridial system of Earthworms. 
In my paper upon Perichseta (1) I pointed out that the 
facts therein described were in favour of the assumption 
that the presence of a single pair of nephridia per segment 
(e. g. in Lumbricus) was the last stage of a reduction of an 
excretory system like that of Perichaeta; and that the ex- 
cretory system of Perichaeta was distinctly comparable to 
that of the Platyhelminths. With regard to the first point. 
Professor Spencer’s observations are, as he has pointed out, 
decidedly confirmatory of that view. Indeed, the nephridial 
system of Megascolides appears to me to be hardly intel- 
ligible on the hypothesis that Lumbricus represents the 
primitive condition. 
Dr. Hugo Eisig’s magnificent monograph of the Capitellidae 
(15), which has just been published, contains a very detailed 
discussion of the nephridial question. It must be confessed 
that the structure of the nephridia in the Capitellidae might be 
equally well explained on the hypothesis that the ancestral 
condition of the Annelid nephridial system is represented by a 
pair of distinct nephridia in each segment. And this is the 
position which Dr. Eisig takes up. The branching, whether 
of the distal or proximal end of the nephridium, and the 
connection between nephridia of the same segment, as well as 
the multiplication of the latter, he regards as secondary. It 
appears to me that this position may be safely yielded without 
affecting the strength of the converse view which is main- 
tained in the present paper. I believe it to be unnecessary to 
assume that the Oligochaeta and the Polychaeta have been 
derived from the same Annelid stock: I hold that the ancestral 
form from which they diverged was intermediate between the 
Platyhelminths and Annelids. There is no difficulty in drawing 
