THE LEEOCHES OF JAPAN. 347 
the habit of crawling partly or wholly out of the water, when 
the air is so saturated with moisture that it can venture out 
without exposing its skin to undue desiccation. Remembering 
that the respiratory functions in the Leech are performed by 
the skin, and that, provided this is kept moist, it is capable of 
drawing its supply of oxygen from damp air, there is little 
difficulty in understanding how such an animal might become 
accustomed to living out of water altogether. Such a change 
would not lead necessarily to the immediate loss of any organs 
nor to the acquisition of new ones. Certain organs have been 
compelled to do more work in the Land Leech than they do in 
the aquatic Leech, and the consequence has been multiplication 
and enlargement. The skin-glands have become larger and 
more numerous, and the nephridial vesicles have expanded to 
bladder-like reservoirs, so that the Leech is still able to keep 
its dermal respiratory organ constantly moist. 
The Land Leeches are mainly confined to islands and con- 
tinents that lie within the tropics; but the extreme limits of 
their latitudinal distribution is not much less than 40° on each 
side of the equator. The highest parallel of N. lat. is touched 
in Central Japan ; of S. lat. in the southern provinces of Chile. 
Notwithstanding this wide range in latitude, the conditions 
under which the different species live are remarkably uniform. 
From the Himalayas to Japan, from Ceylon to Chiloe, they 
have established themselves in localities that present excep- 
tionally even, and almost identical, conditions of climate. 
Neither in the most northern nor in the most southern lati- 
tudes of their distributional area have they passed much beyond 
a subtropical environment; and within the tropics, the peren- 
nially humid mountain forests in which they have made their 
homes, shield them from the more severe degrees of heat. In 
the Himalayan mountains and in Japan they range somewhat 
above the line at which snow falls annually ; but they are most 
abundant below this line. In Ceylon and most of the remain- 
ing countries inhabited by them they are never exposed to 
snow and ice. The Singhalese species is, however, as I have 
proved by experiment, capable of enduring a temperature as 
