i AQUATIC BEETLES 55 



by stiff pointed hairs. The two large cupules are of 

 unequal size, and carried on stalks which are deeply 

 sunk into the integument. Each ends in an umbrella 

 stiffened by many radiating ribs, which project 

 beyond the edge. The umbrella is elastic, and can 

 be pressed out flat without injury to its shape. The 

 smaller and more numerous cupules exhibit the same 

 structure, but the stalk is longer in proportion, and 

 the umbrella much smaller ; the ribs minute, and 

 enclosed in the web. The enlarged joints of the 

 middle leg of the male are also furnished with many 

 small cupules. Simmermacher l says that the male 

 of Dytiscus marginalis has 170 sucking hairs on each 

 fore leg, and 1590 on each middle leg. 



The adhesive power of the suckers is very great. 

 Plateau 2 found by actual experiment that a Dytiscus 

 marginalis, fresh killed by ether, when its suckers 

 were applied to a cylinder of smooth glass, could 

 support more than thirteen times its own weight. 



Mr. Lowne 3 has pointed out several facts respect- 

 ing the suckers of Dytiscus which have escaped the 

 notice of other observers. The cavity of the tarsus, 

 he says, contains a large sac, which is filled with a 

 gelatinous fluid. The bases of the cupules open into 

 this sac, and pressure upon their free ends causes the 

 fluid to exude. The stalks of the cupules are hollow, 

 and serve as channels for the passage of the fluid. 



1 Zcits.f. wiss. Zool. Bd. XI, p. 493. This memoir contains 

 an excellent account of the suckers of Insects in general, and 

 especially of Dytiscus. 



2 Ann. Entom. Soc. Be/g., Vol. XV. p. 205 (1871-2). 



3 Month. Micr.Journ., Vol. V. p. 267 (1871). 



