254 



ANIMAL COLOKATION. 



(Red Admiral, Peacock, Tortoiseshell, etc.) pi'esent identical 

 tints in both sexes. In others, on the contrary, the colours 

 are so different that they might be taken for different species. 

 The Ghost Swift has white shining wings in the male sex, 

 and brown with orange markings in the female ; the males 

 of the " Blues," for the most part, alone deserve their name, 

 for the females have a prevailing brown colour. Among 

 moths the difference is sometimes reduced to little more than 

 a difference in size — as, for example, the Leopard moth. The 

 female of the Vapourer, Winter moth, and some others (fig. 28) 



Fig. 28.— (', Female of Psyche hdi.c. b, Male, c. Case of the male ; 0., of the female 

 cateipillar. 



have almost completely lost those characteristic organs of the 

 Lepidoptera — the wings. The colours of dragon-fligs some- 

 times differ in the two sexes, and there are plenty of other 

 examples among other insects of the same phenomenon. 



Among the Isopod Crustaceans (of which the common 

 woodlouse is a familiar example), there are secondary 

 sexual differences which seem to be unnecessary, that is to 

 say, they have, or appear to have, no relation to pairing ; they 

 are merely evidence of maleness or femaleness as the case 

 may be. In certain species of Sphferomidse the males have 

 a long spine upon the back — a structure which is entirely 

 wanting in the female. In Ceratocephalus grayanus, a large 



