?32 SEXUAL SELECTION. [Part II. 



abdomen, which ought perhaps to be ranked as primary 

 organs, 2 " it is astonishing," as Mr. B. D. Walsh 3 has re- 

 marked, "how many different organs are worked in by 

 Nature, for the seemingly insignificant object of enabling 

 the male to grasp the female firmly." The mandibles or 

 jaws are sometimes used for this purpose;, thus the male 

 Corydalis cornutus (a neuropterous insect in some degree 

 allied to the Dragon-flies, etc.) has immense curved jaws, 

 many times longer than those of the female ; and they are 

 smooth instead of being toothed, by which means he is 

 enabled to seize her without injury. 4 One of the stag- 

 beetles of North America {JLucanus elaphus) uses his jaws, 

 which are much larger than those of the female, for the 

 same purpose, but probably likewise for fighting. In one 

 of the sand-wasps (Ammophila) the jaws in the two sexes 

 are closely alike, but are used for widely-different pur- 

 poses ; the males, as Prof. Westwood observes, " are ex- 

 ceedingly ardent, seizing their partners round the neck 

 with their sickle-shaped jaws ; " 6 while the females use 



2 These organs in the male often differ in closely-allied species, and 

 afford excellent specific characters. But their importance under a func- 

 tional point of view, as Mr. R. MacLachlan has remarked to me, has 

 probably been overrated. It has been suggested, that slight differences 

 m these organs would suffice to prevent the intercrossing of well-marked 

 varieties or incipient species, and would thus aid in their development. 

 That this can hardly be the case, we may infer from the many recorded 

 cases (see, for instance, Bronn, 'Geschichte der Natur,' B. ii. 1843, a. 

 164 ; and Westwood, 'Transact. Ent. Soc.' vol. iii. 1842, p. 195) of dis- 

 tinct species having been observed in union. Mr. MacLachlan informs 

 me (vide 'Stett. Ent. Zeitung,' 1867, s. 155) that when several species of 

 Phryganidae, which present strongly-pronounced differences of this kind, 

 were confined together by Br. Aug. Meyer, they coupled, and one pair 

 produced fertile ova. 



3 ' The Practical Entomologist,' Philadelphia, vol. ii. May, 1867, p. 88. 



4 Mr. Walsh, ibid. p. 107. 



5 ' Modern Classification of Insects,' vol. ii. 1840, pp. 206, 205. Mr. 

 Walsh, who called my attention to this double use of the jaws, says that 

 he has repeatedly observed this fact. 



