SEX-CHARACTERS ILLUSTRATED 67 



(Lucanidae) the mandibles of the males are 

 sometimes as long as the body, and, like the 

 antlers of stags, they often seem to be very 

 much in the way. Darwin called particular 

 attention to the great differences in the degree 

 of development of the male excrescences in 

 beetles, some species having them in extra- 

 ordinary exuberance while others show no 

 dimorphism to speak of. In some cases, as 

 in many moths, the female beetles are sluggish 

 and have no wings. In the glow-worm (Lam- 

 pyris noctiluca) the males have well-developed 

 wings and very large eyes ; the female has 

 smaller eyes and no wings. Among spiders, 

 the males are often pigmies compared with 

 their mates, and often much more brilliantly 

 coloured. It has been calculated that the 

 disproportion of size is sometimes such as 

 would be observed if a man 6 ft. high and 

 150 Ib. in weight were to marry a giantess of 

 80 ft. in height and 200,000 Ib. in weight 

 (see Fig. 2). 



Among Crustaceans sex-dimorphism is 

 common, even if we do not take into account 

 the extraordinary cases in which the female 

 is parasitic and the male free-living. One of 

 the most striking cases is that of the giant 

 crab (Macrocheira) of Japanese waters, where 

 the male has huge forceps many times longer 

 than the body, while the female is very much 

 smaller and has the forceps unexaggerated. 

 Many male crustaceans have specially de- 

 veloped clasping organs and are often larger 

 than their males. Every one knows the 

 common Gammarus of the shore, where the 

 male is much larger and stronger than his 



