THE LEECHES OF JAPAN. 333 
Leeches has enabled me to identify at least three of the four 
rings. I find that segmental papille are sometimes quite 
distinct, not only on the 93rd ring, as shown in the figure, but 
also on the 94th and 95th. I have not detected any satis- 
factory traces of these papillz on the 96th ring, which is the 
last and most rudimentary of all the rings. The discovery of 
papillz on the 94th and 95th, not only in this species, but 
also in the Singhalese and the Australian species, makes it 
certain that the four posterior rings do not represent one 
somite, but at least three, which would raise the total number 
to twenty-five. As the 93rd, 94th, and 95th rings each repre- 
sent a somite, it is more than probable that the 96th ring 
represents a remuant of the papillate ring of the 26th somite. 
The rings may then be identified as follows: 
93rd ring (Land Leech) = 94th (Medicinal Leech). 
94th ” ” = 97th 2» 
95th ,, a == 99th Ps 
96th ,, ‘ == I0lst * 
Thus five rings have been lost behind and only one in front. 
The loss at the anterior end is correlated with a higher deve- 
lopment of the sense-organs; at the opposite end, with the 
enlargement of the acetabulum and the hind end of the body. 
At both extremities the sacrifice of rings have been restricted 
to the less important; and it is plain that the less specialized 
rings of the hind end have been the first to disappear. It is 
the hind end of the body that has undergone the greater 
changes in adaptation to life on land. 
In abandoning aquatic life, the Land Leech became restricted 
to one of the two modes of locomotion open to it while living 
in the water ; henceforth the practice of swimming was discon- 
tinued, while that of creeping was enormously increased to 
meet the requirements of the new conditions of life. The 
result was that the ability to swim was finally completely lost, 
while that of creeping was immensely improved. Adaptive 
changes in size, form, and proportions advanced pari passu 
with the cultivation of one mode of locomotion to the exclu- 
sion of the other. The centre of gravity travelled backward 
VOL, XXVI, PART 3.—-NEW SER, Z 
