THE LEEOHES OF JAPAN. 329 
for then they will be induced to take a position as far as 
possible from the mouth, and new specimens may be added 
without giving those already in time to escape. 
In moving about, the cephalic lobe is much elongated, and 
its obtusely pointed tip appears to be used as an organ of 
touch. The annuli of the anterior portion of the body are at 
the same time more prominent and the eyes more protuberant. 
The mode of progression is the creeping movement common to 
all Leeches. The head is thrown forward as far as the extended 
body will permit, and the oral sucker having been fixed the 
body is drawn up into a vertical loop, and the posterior sucker 
placed close to the anterior. These looped strides may be 
repeated with such rapidity as to give the appearance of jump- 
ing, but such a movement is plainly impossible in this mode of 
locomotion. 
Comparison of the Land Leech with the Medicinal 
Leech.—A comparison of the Land Leech with the Japanese 
Medicinal Leech, which agrees in all its leading features with 
the continental varieties of Hirudo, affords unmistakable evi- 
dence of genetic relationship between the two genera. 
In both the land and the aquatic Leech we find that the 
typical somite embraces five rings ; but the two species show a 
difference of at least five in the total number of rings compos- 
ing the body. This fact might lead one to suspect that the 
Land Leech had lost an entire somite; but a careful study of the 
two cases does not support this view. In Pl. XVIII, fig. 10, I 
have represented the whole number of rings in the Japanese 
Medicinal Leech. The total number of rings may be made to 
vary, apparently at least, according to the mode of counting. 
Most authors count the rings as they are seen on the ventral 
side, beginning with the buccal ring (5th and 6th in my figure), 
and take no account of the fragmentary post-anal ring; thus 
counted there would be but ninety-five rings, which is the 
number usually given for H. medicinalis of Europe. Again, 
if the rings are counted from the dorsal side, leaving the 
ventral aspect entirely out of consideration, we find that the 
buccal and post-buccal are each double, and must be counted 
