396 Cc. O. WHITMAN. 
of this area is not very sharp. Possibly it represents the 
terminal portion of a nerve, but I have obtained no evidence 
in support of this view. 
The small oval or elliptical nucleus (n.) is usually found at 
the base of the thickened portion of proptoplasm. 
Function.—Hbrard ventures the following suggestion as to 
the function of the segmental papilla. ‘Ilse pourrait que ces 
parties fussent les analogues rudimentaires des houppes respi- 
ratoires ou autres que plusieurs des annélides dorsi-branches, 
je citerai les amphinomes, portent sur chacun des anneaux 
du corps.” 
I have shown that they are sense-organs, and that from 
them the eyes have developed. I have not discovered any 
sense-hairs belonging to these organs, but I have found that 
a branch of the lateral nerves runs to each of them. For 
reasons before mentioned, I think it probable that they repre- 
sent incipient eye-spots. 
Postscript. 
The unavoidable delays that have prevented the earlier 
publication of this paper have afforded time for a renewed 
study of the segmental sense-organs; and the results obtained 
enable me both to enlarge and to modify to some extent 
my general conclusions on their function. These conclu- 
sions, as presented in the foregoing pages, were based first 
of all on the serial homology of the segmental sense-organs 
with the eyes, and second on their structure as ascertained 
from sections of the Land Leech. A study of these organs in 
Clepsine has thrown new light on their structure in Hirudo 
and closely-allied genera. By the aid of a few diagrams I 
shall endeavour to make clear their more prominent features 
in both classes of Leeches, and shall then offer a few further 
considerations relative to their function. I find only six 
distinct rows of segmental sense-organs on the dorsal side of 
Clepsine, corresponding to the median, inner lateral, and 
outer lateral of Hirudo. | 
On the ventral side, where they are much smaller and more 
