Chap. X. 
INSECTS. 
343 
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 circumstance that the females of some water* 
beetles (Dytiscus) have their 
elytra deeply grooved, and 
in Acilius sulcatus thickly set 
with hairs, as an aid to the 
male. The females of some 
other water-beetles (Hydro- 
porus) have their elytra 
punctured for the same ob- 
ject. 6 In the male of Crabro 
cribrarius (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 appear- 
ance like that of a riddle. 7 
In the male of Penthe (a 
genus of beetles) a few of Fig. 8. Crabro cribrarius. Upper figure 
the middle joints of the an- male; lower figure ’ “ 
tennse are dilated and furnished on the inferior surface 
6 We have here a curious and inexplicable case of dimorphism , r 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 4 Zoologist/ 
vol. v.-vi. 1847-48, p. 1896. Also Kirby and Spence, ‘Introduction to 
Entomology/ vol. iii. 1826, p. 305. 
7 Westwood, ‘ Modern Class.’ vol. ii. p. 193. The following state- 
ment about Penthe, and others in inverted commas, are taken from 
Mr. W r alsh, 'Practical Entomologist/ Philadelphia, vol. ii. p. 88. 
