THE LEECHES OF JAPAN. 395 
The same is true of the second, third, and fourth pairs of eyes. 
The first pair of eyes (oc 1) occupy the place of two median 
papille (m.), unless the appearances are deceptive. It is, of 
course, possible that the median papille of this ring have been 
lost, and that the eyes have developed from inner lateral 
papillae. The appearances seem to me to favour the opinion 
that they have been derived from a pair of median papille. 
The papille are not round, but oval, and inclined as in Hiru- 
dinaria javanica (fig. 56, Pl. XX). 
The median papille are arranged in metameric pairs, and 
the distance between the two rows is about the same as that 
between the first two eyes. Between the two rows of lateral 
papille on each side the distance is about half as great as 
between the inner lateral row and the median row. The 
marginal papille are placed at the extreme edge of the body. 
The outer lateral papille (o/.) are not recoguisable on the 
first ring, and the marginal papille are absent on the Ist and 
2nd rings; but their presence on the remaining rings (3rd, 
5th, and 8th) makes it plain that ali the eyes, except perhaps 
the first pair, occupy the place of the inner lateral papille. 
Structure.—In comparing the Land Leech with the Medi- 
cinal Leech, I have already described the structure of the 
segmental papillae. Sections of Macrobdella throw some light 
on the nature of what I have called the “ white corpuscle ” in 
the large clear cells which form the central portion of the eye, 
and which are associated with the segmental papille and with 
the “ goblet-shaped ” organs of the lip. 
- Fig. 71, Pl. XXI, shows two of these cells from the 
eye. In one of these the “ white corpuscle” appears in the 
form of three bubble-like vesicles or vacuoles. In some cells 
I find as many as six of these spherical vacuoles, each bounded 
by a thin but distinct film. These spaces contain a watery 
fluid which does not stain in the least. The protoplasm of 
the cells is granular, and forms a peripheral layer, thickened 
on one side, as shown in Leydig’s figures. In this thickened 
portion which projects into the vacuolar space, may be seen a 
small oval area, somewhat more darkly shaded. The outline 
