30 ALFRED GIBBS BOURNE. 
have examined, so that even if they were all connected together 
into a network and did not develop, as they appear to do, we 
should have a condition very different from that of Pontobdella, 
and much more nearly connected with a meganephric condition. 
(4) I knew that in Pericheta pellucida and some other 
species which, although not to be placed, strictly speaking, in 
the same genus as P. aspergillum, P. mirabilis, &c., are 
very closely allied forms, one pair only of nephridia were to 
be found in any segment, which rendered it, at any rate, un- 
likely that anything so fundamentally different from the mega- 
nephric condition as the plectonephric condition would occur. 
(The existence of Perichetes with meganephridia reopens the 
question of the systematic position of Perionyx.) 
I think that the condition of the nephridium in Perichetes, 
Acanthodrilus, and many other genera must have arisen from 
the meganephric condition. That the funnel appears, as in 
Mahbenus and Megascolides, only to disappear, and that the 
loop which appears earliest in the nephridia which develop 
first and attains such great complication, only to be arrested in 
its development or even to abort, to set aside all other con- 
siderations, is very strong evidence that the development of 
micronephridia by budding from it, is a specialised condition. 
Taking into account what we know of the development of 
the nephridia in other leeches and the presence of funnels (if 
M. Bolsius will allow me to call them so), so seemingly out of 
keeping with the rest of the nephridium in Pontobdella, I 
shall not be surprised to learn from a history of its develop- 
ment that that is by no means a primitive structure, and has 
possibly no genetic relationship with the tubules of Platy- 
helminths. 
I am unable at present to bring forward any direct evi- 
dence as to the relationship between genital ducts and 
nephridia in earthworms, but I cannot refrain upon this 
occasion from pointing out that the demonstration of the fact 
that a so-called plectonephric condition is not a primitive one 
removes the strongest objection to the theory brought forward 
by Lankester in one of his earliest contributions to this Journal. 
