DEVELOPMENT OF ACANTHODRILUS MULTIPORUS. 531 
may be remarked, the nephridia occupy two segments; but the 
position of the funnel, as well as of the external pore, is 
different. In the development of Acanthodrilus multi- 
porus I have pointed out that the apertures of the mucous 
glands gradually shift backwards with the brain until they are 
placed well within the buccal cavity, instead of only just within 
it: it is quite possible that in an earlier stage still they are 
outside of it. Ifthe aperture belongs to the prostomium it is 
perhaps inevitable that with the ingrowth of the stomodzeum 
they should come ultimately to lie within the buccal cavity. 
The prostomium of these embryos, as of the embryo Lum- 
bricus, is inconspicuous; but fig. 22 looks very much as if 
the aperture of the first pair of nephridia is in reality upon 
the prostomium. In this case the apparent difference in posi- 
tion between the nephridiopores of the first pair and of those 
which follow can be understood. 
I think that there can be no doubt as to the homology 
between these nephridia and the provisional first pair of 
Lumbricus; and they are certainly not different from the 
nephridia which follow, except that they occupy two segments. 
I have referred to the difficulty of comparing the first pair of 
pronephridia to those which follow, by reason of the fact that 
they occupy two segments in Lumbricus; and also to Vejdov- 
sky’s suggestion that they are able to extend backwards 
through the incompleteness of the septa. The same explana- 
tion will suit Acanthodrilus perfectly well, so far as these 
facts are concerned. 
Later on a complication ensues in the fusion of the 
first and second nephridia, the compound organ having two 
funnels.’ 
1 Tn connection with this I may refer to the mucous gland of Urocheta; 
I described that organ as extending through several segments (which Perrier 
first pointed out), and as furnished with several funnels. Dr. Rosa has lately 
pointed out (25) certain discrepancies between my descriptions and figures. On 
again looking into the matter I find that Rosa is right, and that the mucous 
gland opens on to the anterior margin of the first setigerous segment; and 
that an interval of a segment occurs between the pore of the mucous gland 
and that of the first nephridium, i. e, the latter is upon the third setigerous 
