INSECTS 



255 



little is known of the life-histories of these forms and of their 

 habits it is premature to conclude that they are inexplicable. 

 In the Lucanidae the peculiarity of the males consists in 

 the enlargement of the true mandibles, which are sometimes 

 as long as the body and give rise to the popular name of 

 stag-beetles. These organs also, according to Mr. Sharp, are 

 of very little use ; but it is known, as stated by Darwin, that 

 male stag-beetles fight fiercely with their great mandibles, 

 and they have often been seen carrying off the females with 



A 





Fig. 25. Lueanus cervus the common Stag-beetle. A, male ; B female. 



them. Thus I see no difficulty in attributing the great 

 hypertrophy of the mandibles to the violent use which is 

 made of them, which on the one hand enlarges the muscles 

 and the cuticle to which the muscles are attached, and on the 

 other causes the epidermis to be hypertrophied, so that 

 the whole appendage grows larger and the cuticle thicker. 

 Darwin gives striking figures of the male and female of 

 Chiasognathus Grantii, one of the Lucanidse found in Chili, 

 and states from his own observation that the greatly enlarged 

 mandibles of the male are used as weapons. He also describes 



