THE LEECHES OF JAPAN. 4.07 
in which the goblet-shaped organs are located, is plainly used 
as an organ of touch. 
I have never seen any evidence that the eyes are employed 
either for taste or touch, and the observations of Ranke on this 
point appear to me to have little value. If the structure of the 
eye is what I have represented it to be, it is plain that it is 
not adapted for receiving images of external objects. At most 
there can only be the power of distinguishing light from dark- 
ness, and this power the Leech certainly possesses. 
There is still much uncertainty respecting the functional 
nature of the segmental sense-organs. It is quite certain, 
however, that they do not serve the same purpose as the 
lateral-line organs of the Fish or the segmental sense-organs of 
the Capitellide. This point is made certain in two ways; 
first, by the absence of sense-hairs, and second, by the fact 
that Land Leeches are provided with these organs. It seems 
also quite clear that their chief function is not that of tactile 
organs, for they are not more sensitive to touch than other 
parts of the epidermis. ‘Their structure is in some respects 
much like that of organs of taste, but they certainly could not 
serve the Land Leech in this capacity. Excluding then the 
three senses of touch, taste, and hearing, there remain those 
of sight and smell, both of which would be very useful to both 
land and aquatic Leeches. The eyes are undoubtedly visual 
organs, but they alone are not sufficient for the obvious needs 
of the Leech. One of the most characteristic habits of Leeches 
in general is that of keeping themselves in dark or shaded 
places. It is not enough to screen the head from the light ; 
the whole body, including the posterior sucker, require to be 
so protected in order to satisfy fully the usual conditions of rest. 
This is particularly true of Clepsine and Hirudo, and only a 
little less so of Nephelis. 
But how is it possible for Leeches to know when these con- 
ditions are fulfilled for all parts of the body? This question is 
answered, if the segmental sense-organs are capable of dis- 
tinguishing light and darkness. The massive development of 
the large clear cells in the eyes is very conclusive evidence that 
