THE LEECHES OF JAPAN. 343 
result. We have then experimental proof that the Leech can 
moisten its ventral surface at least with fluid discharged from 
its nephridia. If the loss of moisture stimulates a Leech to 
expel its nephridial fluid, the most natural inference seems to 
be that the act is designed to restore the moisture. I can see 
no serious objection to the opinion that the nephridia may co- 
operate with the numerous gland-cells opening at the surface 
in keeping the skin moist; and I am unable, on any other 
hypothesis, to find a satisfactory explanation of the peculiar 
differences between the nephridia of the aquatic Leech and 
those of the Land Leech. These peculiarities were undoubtedly 
acquired in adaptation to terrestrial life—a mode of life which, 
under the most favorable conditions, must inevitably have 
taxed to"the utmost any organs that could furnish moisture or 
serve as reservoirs. We are not therefore surprised to find 
the Land Leech provided with more numerous skin-glands and 
more capacious nephridial vesicles than its nearest aquatic 
relative. 5; 
Allowing that the nephridial secretion may serve the end we 
have indicated, and remembering that such service would most 
likely be required when the Leech is scouring about, it is plain 
that the marginal position of the nephridial pores would 
present some advantages over the latero-ventral position seen 
in Hirudo. The various attitudes assumed by the Leech while 
moving about are such as would favour the spreading of the 
secretion in all directions, over the dorsal as well as the ventral 
surface. 
Under the head of “ habits,” I have mentioned that while 
the Land Leech is engaged in the act of sucking blood, it dis- 
charges a limpid fluid in such quantities that it rolls away in 
several drops. I have supposed that this fluid came from two 
sources, namely, the mucous gland-cells and the nephridia. 
Gratiolet appears to have observed precisely the same pheno- 
menon in the Medicinal Leech; and he was of the opinion that 
the fluid came from the nephridia. As the gland-cells are 
undoubtedly active when the Leech is thus engaged, it does not 
seem probable that the escaping fluid contains no admixture of 
