THE LEECHES OF JAPAN. 341 
tion of the gland-cells of the clitellum the work of forming 
the cocoon, and serving, on the other, in common with the 
fluid discharged from the uterus, as reserve food-material for 
the young, is a supposition neither probable in itself nor well 
supported by observation. By what means could the Leech 
gather the renal fluid around the clitellum? And, allowing that 
this could be accomplished, by what process could the fluid be 
converted into the spongy substance of the cocoon? That 
such a transformation requires some explanation is evident 
from the fact that the fluid does not take the form of a spongy 
body on other parts of the body. Leuckart! has shown conclu- 
sively that both the capsule and its spongy mantle are of the 
same chemical and physical nature; and the manner in which 
the cocoon is formed leaves little room to doubt that its 
substance is derived exclusively from the unicellular glands of 
the clitellum. This is the view taken by Leuckart, Lankester,? 
and, so far as I know, by all the more recent writers. 
That the nephridia within the limits of the clitellum concur 
with the uterus in supplying the fluid contents of the cocoon, 
seems to me not altogether improbable, in view of the pecu- 
liarities of the vesicles of this region in the Land Leech. The 
only observation in favour of this opinion adduced by Hbrard 
is the following :—A single Leech was opened at the moment 
when the capsule was nearly ready for the reception of the 
eggs ; and the vesicles within the clitellum, and within this 
region only, were found full of fluid; the same vesicles were 
found empty in another individual that had just deposited a 
cocoon. Perhaps we shall not show too little respect for an 
opinion based on a single experiment of this kind, if we venture 
to express a regret that Hbrard did not, so far as can be learned 
from his statements, repeat his observation before giving it the 
importance of a general fact. 
In the Medicinal Leech, the fourth, fifth, and sixth pairs of 
vesicles lie within the sexual girdle, precisely as in the Land 
Leech ; but their structure is the same as that of the vesicles 
1 *Die Menschlichen Parasiten,’ i, p. 684, 1863. 
2 ‘Quart. Journ. Mic, Sci.,’ xx, p. 304. 
