104 EXTERNAL CONDITIONS OF VITAL ACTIVITY. 



about. In like manner it is observed that the rainy season, between 

 the tropics, brings forth the hosts of insects, which the drought had 

 caused to remain inactive in their hiding-places. Animals thus rendered 

 torpid seem to have a tendency to bury themselves in the ground, like 

 those which are driven to winter quarters by cold. Mr. Darwin men- 

 tions that he observed with some surprise at Rio de Janeiro, that, a few 

 days after some little depressions had been changed into pools of water 

 by the rain, they were peopled by numerous full-grown shells and beetles. 

 161. This torpidity consequent upon drought is not confined to In- 

 vertebrated animals. There are several Fish, inhabiting fresh water, 

 which bury themselves in the mud when their streams or pools are dried 

 up, and which remain there in a torpid condition until they are again 

 moistened. This is the case with the curious Lepidosiren, which forms 

 so remarkable a connecting link between Fishes and the Batrachian Rep- 

 tiles : it is an inhabitant of the upper parts of the river Gambia, which 

 are liable to be dried up during much more than half the year; and the 

 whole of this period is spent by it in a hollow which it excavates for 

 itself deep in the mud, where it lies coiled up in a completely torpid 

 condition, whence it is called by the natives the sleeping-fish. When 

 the return of the rainy season causes the streams to be again filled, so 

 that the water finds its way down to the hiding-place of the Lepidosiren, 

 it comes forth again for its brief period of activity ; and with the ap- 

 proach of drought, it again works its way down into the mud, which 

 speedily hardens around it into a solid mass. In the same manner, the 

 Proteus, an inhabitant of certain lakes in the Tyrol, which are liable to 

 be periodically dried up, retires at these periods to the underground pas- 

 sages that connect them, where it is believed to remain in a torpid con- 

 dition ; and it thence emerges into the lakes, as soon as they again be- 

 come filled with water. The Lizards and Serpents, too, of tropical 

 climates appear to be. subject to the same kind of torpidity, in conse- 

 quence of drought, as that which affects those of temperate regions 

 during the cold of winter. Thus Humboldt has related the strange acci- 

 dent of a hovel having been built over a spot where a young Crocodile 

 lay buried alive, though torpid, in the hardened mud; and he mentions 

 that the Indians often find enormous Boas in the same lethargic state ; 

 and that these revive when irritated or wetted with water. All these 

 examples show the necessity of a fixed amount of fluid, in the animal 

 structure, for the maintenance of vital activity : whilst they also demon- 

 strate, that the preservation of the vital properties of that structure is . 

 not always incompatible with the partial, or even the complete abstrac- 

 tion of that fluid ; the solid portions being then much less liable to de- 

 composition than by heat, or by other agencies, than they are in their 

 ordinary condition. 



