19S 
EDWIN S. (iOODKICH. 
groove backwards to the pharynx into which it opens. 
Very numerous solenocytes are set chiefly on short blind 
diverticula. It has no internal opening, and lies in a cavity, 
Avhich is in communication with the myocoele of the first 
myotome in the larva. 
That this nephridium is in every way similar to and homo- 
logous with the paired posterior nephridia there can be no 
doubt. Van Wijhe’s suggestion, mentioned above, must 
therefore be abandoned. Two peculiarities, however, still 
remain to be explained ; its unpaired character and its open- 
ing into the alimentary canal. No one, so far as I am aware, 
has yet worked out the exact relation of the gill-slits to the 
somites in the larva of Amphioxus, and my own observations 
on this point are very incomplete. But judging from the 
course of the dorsal spinal nerves (fig. 30), the first gill-slit, 
of the left (on the right side) series, which is the first to 
appear in the larva, corresponds to the third myotome. 
Probably its true morphological position is between the 
second and third myotome. Presumably Hatschek’s nephri- 
dium would correspond to the next gill-slit in front, between 
the second and first myotonies, did such a slit exist. As for 
its unpaired character, I can for the present offer no better 
explanation than this, that it is the left of an original 
anterior pair of nephridia, the one-sided development of 
which is no doubt correlated with the general asymmetry of 
the anterior region so conspicuous in the larva. But this 
question can only be profitably discussed after an exhaustive 
study of the development, and must therefore be put aside 
for the pi’esent. In the same way a detailed knowledge of 
the development of this organ, and of the posterior nephridia, 
is necessary before one can discuss the significance of the 
anomalous position of the opening. 
