vil ABYSSAL AND SUBTERRANEAN FORMS 209 
produced which lie dormant during the winter. The pelagic 
Copepods may either produce resting eggs for the winter 
(Diaptomus), or else the winter is passed through in the 
Nauplius stage, the larvae hibernating in the mud until the 
spring (Cyclopidae). 
We have so far only dealt with fresh-water Entomostraca. 
There are, in addition, a number of Malacostraca which inhabit 
fresh water, and some of these are found in the abyssal region 
of the great lakes, which must now be considered. 
The physical conditions of the abyssal region are still more 
stable than those of the pelagic region, since the water is never 
disturbed, the bottom is always composed of a fine mud, the 
temperature is constant at 4°-5° C., and there is a total absence 
of light. It was hardly expected that animals would inhabit 
this region, until Forel discovered Asel/us aquaticus in a depth of 
forty metres in the Lake of Geneva, and subsequently showed 
that quite a number of animals, including a Hydra, several 
worms, Molluscs, Crustacea, and larval Insects, may be found in 
these or even much greater depths. 
The Crustacea of the abyssal region are two in number, and 
these have been found in a number of European lakes ; Miphargus 
puteanus, a blind Amphipod closely allied to Gammarus; and 
Asellus forelit, alhed to A. aquaticus and A. cavatieus, which 
may be either quite blind or else retain the rudiments of eyes. 
These two Crustacea, under a practically identical form, are 
also found in the subterranean waters of Europe, and Forel 
considers that they have arrived in the abysses of the lakes 
from the subterranean channels, and are not derivatives of the 
littoral fauna." 
Having completed our short review of lacustrine Crustacea, 
we may deal with the subterranean and cave Crustacea,’ which, 
as far as light and temperature are concerned, are subjected to 
very similar conditions to those dwelling at the bottom of deep 
lakes. The inhabitants of the subterranean waters have been 
chiefly brought to light in Artesian wells, ete., while the cave- 
1 
* Mr. C. H. Martin points out to me that in the Scottish lochs, which from their 
geological nature are evidently not connected with subterranean waters, none of 
them nor similar forms occur ; nor do they in the Tasmanian lakes which are on 
igneous diabase, so that Forel’s conclusion would seem to be of wide application. 
2 See Chilton, Trans. Linn. Soc. (2) vi., 1894, p. 163, with review of literature. 
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