Chap. X.] 



INSECTS. 



333 



these organs for burrowing in sand-banks and making 

 their nests. 



The tarsi of the front-legs are dilated in many male 

 beetles, or are furnished with broad cushions of hairs ; 

 and in many genera of water-beetles they are armed with 

 a round flat sucker, so that the male may adhere to the 

 slippery body of the female. 

 It is a much more unusual cir- 

 cumstance that the females of 

 some water-beetles (Dytiscus) 

 have their elytra deeply 

 grooved, and in Acilius sul- 

 catus thickly set with hairs, 

 as an aid to the male. The 

 females of some other water- 

 beetles (Hydroporus) have 

 their elytra punctured for the 

 same object. * In the male of 

 Crabro crihrarius (fig. 8), it is 

 the tibia which is dilated into 

 a broad horny plate, with mi- 

 nute membraneous dots, giv- 

 ing to it a singular appearance 

 like that of a riddle.' In the 

 male of Penthe (a genus of 

 beetles) a few of the middle joints of the antennae are 

 dilated and furnished on the inferior surface with cushions 

 of hair, exactly like those on the tarsi of the Carabidas, 



^ We have here a curious and inexplicable case of dimorphism, for 

 some of the females of four European species of Dytiscus, and of certain 

 species of Hydroporus, have their elytra smooth ; and no intermediate 

 gradations between sulcated or punctured and quite smooth elytra have 

 been observed. See Dr. H. Schaum, as quoted in the ' Zoologist,' vol. 

 v.-vi. 1847-48, p. 1896. Also Kirby and Spence, 'Introduction to En- 

 tomology,' vol. iii. 1826, p. 305. 



' Westwood, ' Modern Class.' vol. ii. p. 193. The following statement 



Fig. 8.— Crabro cribrarius. Upper 

 figure, ma;e ; lower fii,'ure, female. 



