INSECTS. 



313 



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 (Dytis- 

 cus) 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 Crabro cribrarius (fig. 9) it is the 

 tibia which is dilated into a broad horny 

 plate with minute membraneous dots, giving 

 to it a singular appearance like that of a 

 riddle, f 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, ex- 

 actly like those on the tarsi of the Carabidaa, 

 "and obviously for the same end." In 

 male dragon-flies, "the appendages at the 

 tip of the tail are modified in an almost in- 

 finite 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 thick- 

 ened, but this is by no means invariably a 

 sexual character; or one pair, or all three 

 pairs are elongated, sometimes to an extrava- 

 gant length. | 



The sexes of many species in all the orders 

 present differences, of which the meaning is 

 not understood. One curious case is 



1g. 10. Taphro- 

 deres distortus 

 (enlarged). Up- 

 per figure, male; 

 lower figure, 

 female. 



* We have here a curious and inexplicable casfi of dimorphism, for 

 some of the females of four European species of Dysticus, and of 

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

 intermediate gradations between the sulcated or punctured, and the 

 'juite smooth elytra have been observed. See Dr. H. Schaum, as 

 quoted in the " Zoologist," vols. v-vi, 1847-48, p. 1896. Also Kirby 

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



fWestwood, "Modern Class.," vol. ii, p. 193. The following 

 statement about Penthe, and others in inverted commas, are taken 

 from Mr. Walsh, "Practical Entomologist," Phila., vol. iii, p. 88. 



\ Kirby and Spence, " Introduct.," tc., vol. iii, pp. 382-336. 



