564 



THE DESCENT OF MAN 



sucker, so that tlie male may adhere to the slippery body 



of the female. It is a much more unusual circumstauce 

 that the female 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 

 (Hydroporus) have their elytra punctured for 

 the same purpose." In the male of Grahro 

 crihrarius (Fig. 9), it is the tibia which is 

 dilated into a broad horny plate, with minute 

 membranous dots, giving to it a singular ap- 

 pearance like that of a riddle.' In the male of 

 Penthe (a genus of beetles) a few of the middle 

 pints of the antennae are dilated and furnished 

 on the inferior surface with cushions of hair, 

 exactly like those on the tarsi of the Carabidae, 

 "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 embrace 

 the neck of the female. ' ' Lastly, in the males 

 of many insects, 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 



roderes distortus to an extravagant length." 



Upper figure! The sexes of many species in all the orders 



male; lower fig-ure, ^ tpc i i • i j.i 



female. present diiierences or which the meaning is 



not understood. One curious case is that of a beetle (Fig. 10), 



* "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 

 the sulcated or punctured and the quite smooth elytra have been observed. 

 Bee Dr. H. Schaum, as quoted in the "Zoologist," vol. v.-vi., 1847-48, p. 1896. 

 Also Kirby and Spence, "Introduction to Entomology," vol. iii., 1826, p. 305. 



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

 about Penthe, and others in inverted commas, are taken from Mr. Walsh 

 "Practical Entomologist," Philadelphia, vol. ii. p. 88. 



• Kirby and Spence, "Introduct," etc., vol. iii. pp. 332-836. 



? 



