338 Cc. O. WHITMAN. 
The distribution of the large clear cells, each with its 
enigmatical band-shaped corpuscle and minute nucleus, among 
the different sense-organs, appears to show that they are 
sense-cells, and to throw considerable doubt on the com- 
monly received opinion that they function merely as a corpus 
vitreum in the eye of the Leech. The fact that the optic 
nerve, after penetrating the eye, can be traced for some 
distance along its axis between these cells is in itself sufficient 
evidence that they cannot be explained as a purely dioptric 
apparatus (cf. Postscript). 
The Nephridia.—The nephridial organs agree in the main 
with those of the Medicinal Leech, which have been so well 
described by Bourne,! but differ from them in three important 
particulars. 1. The efferent ducts terminate in the margin of 
the body, instead of on the ventral surface at some distance 
from the margin. 2. The vesicles are much larger than in the 
aquatic Leech. 3. The three pairs of vesicles located within 
the region of the clitellum are lined with very thick cubical 
cells which form irregular folds, projecting into the cavity, 
while they are elsewhere lined with thin pavement epi- 
thelium. 
In the European Hirudo, the vesicles are oval sacs, the 
larger diameter of which is only about twice that of the testi- 
cular sacs, and are located just outside the vasa deferentia, 
the successive pairs alternating with the testes. In the Land 
Leech the vesicles are capacious sacs holding the same serial 
relation with the testes, and lying partly beneath, but mainly 
external to, the ceca of the stomach. As they are opposite, 
and continuous with, the ceca, their shape conforms in the 
main to that of these appendages, and hence must vary accord- 
ing to the degree of distension of the latter. In a horizontal 
section of the Leech, one of these vesicles is seen to extend in 
an antero-posterior direction through from three and a half to 
four rings; while in Hirudo it bridges only two rings, less than 
1 A.G. Bourne, (a) On the Structure of the Nephridia of the Medicinal 
Leech,” ‘Quart. Journ. Mic. Sci.,’ xx, July, 1880, p.283. (4) ** The Central 
Duct of the Leech’s Nephridium,” idem., vol. xxii, July, 1882, p. 337. 
