258 SEXUAL DIMORPHISM 



when they reach the stage of the imago will be sterile, either 

 absolutely or comparatively. The testes being absent or 

 imperfectly developed, the unisexual excrescences which are 

 correlated with them will be absent or imperfectly developed. 

 When the modification in the male has been the alteration 

 in shape of mandibles already present in the female, the 

 imperfect development of the testes will naturally imply the 

 development of a male similar to the female. 



In support of this view it may be pointed out that the 

 variations in the development of horns and mandibles in these 

 male Coleoptera resemble very suggestively the variations 

 produced in the horns of stags by partial or complete castra- 

 tion. Therefore it seems reasonable to conclude that in these 

 insects there is a kind of natural castration or sterility of 

 varying degree. With regard to the influence of food on the 

 generative organs, especially of nitrogenous food, it is now 

 well established that the ovaries of bees are prevented from 

 perfect development, or allowed to take that development, 

 according to the food supplied to the larvse. The Termites 

 again develop the sexual organs at almost any stage of de- 

 velopment by means of special feeding. 



The hypothesis that the least differentiated males of these 

 Coleoptera are sterile or neuter has been previously con- 

 sidered, and rejected by Leuthner. 1 He writes : " The idea 

 that the so-called degenerated forms should be regarded as 

 neuters was refuted by an examination of the fully developed, 

 and even comparatively large sexual organs, in which not 

 only the chitinous parts, but also the testes and their contents 

 (the spermatozoa), were found to be well developed in the 

 smallest males." But he adds in a footnote that the sper- 

 matozoa could only be observed in the smallest males of 

 Zucanus cervus, the European stag-beetle. Probably he only 

 possessed dead and perhaps dried specimens of other species. 



1 Monograph of the Odontolabini, Trans. Zool. Soc. Lond. vol. xi., 1885. 



