DEVELOPMENT OF ACANTHODRILUS MULTIPORUS. 535 
after the early stages in which the funnel is present and 
functional; whether there is any connection between these 
two facts Ido not know. ‘To a certain extent, therefore, the 
nephridial system of the adult worm is a new formation, for 
which, however, the nephridia of the embryo furnish the 
material. It is not a simple increase in size and complication 
of structure which converts the nephridia of the embryo into 
those of the adult. There is first of all a temporary cessation 
of function (?) in a part of the nephridium—the portion 
nearest to the funnel—which is produced by the disappear- 
ance of the lumen; this part of the nephridium, as well as 
other parts, then grows actively, and a fresh series of aper- 
tures to the exterior are formed. There is quite as much 
change from the nephridia of the earlier stages to those of 
later stages as from the “ pronephridia” (Vejdovsky, 1) of 
Lumbricus to the definitive nephridia. I have pointed out 
in this paper that the mode of development of the genital 
ducts in Acanthodrilus, as compared with Lumbricus, 
seems to show that the paired nephridia of the larval Acan- 
thodrilus cannot be regarded as the exact equivalents of the 
permanent nephridia of Lumbricus. It seems, therefore, 
still possible to believe that, as regards earthworms at any 
rate, a more diffuse arrangement of the nephridia has pre- 
ceded the paired regular arrangement; at the same time it 
appears to be necessary to assume that originally the paired 
arrangement existed, and that the diffuse condition of the 
nephridia was a subsequent modification of this. But in my 
opinion it must still be proved that the paired nephridia of 
Eudrilus, and other earthworms whose development is 
unknown, are homologous with the paired nephridia of the 
larval Acanthodrilus. 
§ Summary of the more Important New Facts 
contained in this Paper. 
(1) Nephridia.—In the youngest embryos these are paired 
tubes opening on to the exterior by the lateral sete, and each 
