AQUATIC BEETLES 59 



tion which was at its first promulgation likely enough. 

 Plateau ^ in particular has pointed out a number of facts 

 hard to be got over, which tell strongly against the 

 old view, (i) Furrows on the elytra diminish instead of 

 increasing the holding power of the suckers. Ground 

 glass and paper do not on trial act so well as polished 

 glass. (2) The suckers of the male are not applied 

 to the furrowed part of the elytra at all, but to 

 the prothorax and the smooth edges of the elytra. 

 (3) Females with smooth elytra occur now and then in 

 England, and the male can hold these as well as the 

 common form. Sometimes the male has furrowed 

 elytra, and it is said that this is apt to be the case in 

 cold ponds, ill supplied with food. Camerano - says 

 that the sculpturing on the elytra of the female is 

 not constant, but becomes less marked in south- 

 ern countries, and Redtenbacher^ adds that around 

 Vienna the smooth females are as common as the 

 furrowed ones. Many new explanations have been 

 offered of the furrowed elytra, but none seem to carry 

 conviction. It is to be noted that the Carabidae 

 (carnivorous land-beetles allied to Dytiscidae) com- 

 monly have furrowed elytra in both sexes. 



The bases of the hind legs are very broad, and 

 soldered to the under side of the body. This increases 

 the rigidity of the body, and also removes the articu- 

 lation of the hind legs from the margin to the centre 

 of the Insect. There is no doubt some mechanical 

 advantage in this, but I am unable to explain what 



1 A?in. Entom. Soc. Belg., Vol. XV. p. 205 (1871-2). 



2 Atti. R. Ace. Torino., Vol. XV. Quoted from Simmermacher. 

 ^ Fauna Austriaca, Die Kdfer. 



