CHAPTER IV. 



EYDRADEPHAOA. 



We have now completed our notices of the Geodeptaga, the v 

 analogues of the land Carnivora among the higher animals, \ 

 and we now come to the Hydradephaga, or carnivorous Beetles I 

 of the water — the whales, porpoises, and seals of the insect ./ 

 world. 



We know that all animals are specially adapted to the life 

 which they have "to lead, and therefore may naturally expect 

 that Beetles which live in the water will be formed very dif- 

 ferently from those which reside on the land, even though that 

 land be constantly wet. Shape, for example, is likely to be 

 altered. We know that the whales, dolphins, and seals, who 

 have to pass either the whole or the greater part of their lives 

 in the water, and to catch in it the living prey on which they 

 feed, become assimilated in shape to the fishes ; and it is likely 

 that insects will obey the same laws as mammals. This is 

 really the case, the shape of all the Hydradephaga being very 

 fish-like, in order to enable them to pass more easily through 

 the water. As there is much more friction in passing through 

 the water than through the air, the Water Beetles, as the Hy- 

 dradephaga are familiarly called, have the various portions 

 of the body fitting closely to each other, so as to leave an 

 uniform smooth and polished surface, something like that of 

 the scaly surface of the fish, the slippery skin of the whales and 

 dolphins, and the close-set fur of the seals. 



The limbs are also modified to suit the special purpose for 

 which they are designed. As these Beetles walk less than they 

 swim, greater provision has to be made for the latter mode of 

 progression. Accordingly, the first and middle pairs of legs are 

 comparatively small and feeble, the strength being thrown 

 into the hinder pair, which are large in comparison with the 



