276 



The Descent of Man. 



Pakt H. 



much more UDUsual circumstance that the female of some "water- 

 beetles (Dytiscus) have their elytra deeply grooved, and in 

 Acilius sulcutus 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 

 purpose.' In the male of Crabru 

 cribrurius (fig. 9), it is the tibia 

 which is dilated into a broad 

 horny plate, with minute mem- 

 braneous dots, giving to it a sin- 

 gular appearance like that of a 

 riddle.' In the male of Penthe 

 (a genus of beetles) a few of the 

 middle joints of the antennse are 

 dilated and furnished on the in- 

 ferior surface with cushions of hair, 

 exactly like those on the tarsi of 

 the Carabidffi, " and obviously for 

 " the same end." In male dragon- 

 flies, " the appendages at the tip 

 " of the tail are modified in an 

 " almost infinite variety of curious 

 " patterns to enable them to em- 

 " brace the neck of the female." 

 Lastly, in the males of many in- 

 sects, the legs 'are furnished with peculiar spines, knobs or 

 spurs ; or the whole leg is bowed or thickened, but this is by no 

 means invariably a sexual character ; or one pair, or all three 

 pairs are elongated, sometimes to an extravagant length.* 



The sexes of many species in all the orders present differences, 

 of which the meaning is not understood. One curious case is 

 that of a beetle (fig. 10), the male of which has the left mandible 

 much enlarged ; so that the mouth is greatly distorted. In 

 another Carabidous beetle, Eurygnathus," we have the case. 



Fig. 9. Crabi o cribrai ius. Upper Hgure, 

 male^ luwer tiguie, female. 



•^ We have here a curious and 

 inexplicable case of dimorphism, for 

 some of the females of four Euro- 

 pean species of Dytiscus, and of 

 ceilain species of Hydroporus, have 

 their elytra sn;ooth ; and no inter- 

 mediate gradations between the 

 huicated or punctured, and the quite 

 smooth elytra have been observed. 

 See Dr. H. Schaum, as quoted in 

 the 'Zoologist,' vol. v.-vi. 1847-48, 

 p. 1896. Also Ivirby and Spence, 



' Introduction to Entomology,' vol. 

 iii. 1826, p. 305. 



' Westwood, 'Modern Class.' vol. 

 ii. p. 193. The following state- 

 ment about Penthe, and others in 

 inverted commas, are taken from 

 Mr. Walsh, ' Practical Entomolo- 

 gist,' Philadelphia, vol. ii. p. 88. 



' Kirby and Spence, 'Introduct.' 

 &c., vol. iii. pp. 332-336. 



° ' Insecta Madorensia,' 1854, p. 

 20. 



