28 ALFRED GIBBS BOURNE. 
macerating a portion of a full-sized embryo in nitric acid. I 
found it impossible to make out all the details. At d. is seen 
the excretory duct, composed of a very regularly arranged series 
of drain-pipe cells; 6. is the apex of the lobe; at ec. the 
arrangement of the tubules is very characteristic,—there is a 
central tubule and a double set of convoluted tubules, shown in 
the figure by single lines ; at a. is the bunch of outgrowths, each 
one of which subsequently elongates to a considerable extent. 
In a Madras species of Acanthodrilus which has scattered 
nephridia in the adult I have found the nephridia to develop 
as paired organs, one pair to each segment, which bears out 
Beddard’s observations upon this genus (this Journal, vol. 
XXxiii, part 4). I have inserted fig. 43 of the 17th nephridium 
from a 10 mm. long embryo of this species, as it showed with 
absolute clearness the exact course of the greater portion of the - 
ductule from the excretory duct d. up to 6.; from thence on- 
wards to the funnel duct the ductule was too fine to be traced. 
I have not yet obtained stages of this species showing the 
development of the micronephridia, but as the process seems 
to be so similar in such widely different forms as Mahbenus 
imperatrix and Megascolides australis it is probably 
the way in which all micronephridia develop. 
The So-called “ Plectonephric” Condition. 
My own observations, those of Vejdovsky, and in a less 
direct way those of Bergh, Wilson, and others who have dealt 
with development of the nephridia in meganephric forms, 
and even those of Beddard himself (on the development of 
A. multiporus), throw grave doubt upon the conclusions 
arrived at by Beddard and Spencer with regard to this matter. 
Apart from this I have for some years, upon anatomical grounds, 
doubted the existence even, of such a condition of the nephri- 
dium as was described by Beddard for P. aspergillum. For 
one thing, Beddard’s figs. 7 and 10 (this Journal, vol. xxviii, 
Pl. XXX) do not seem to me to prove what he would 
have them prove; fig. 10 contains an impossible blood-vessel, 
branching and returning blood into itself, which looks very 
