208 The Descent of Man. Part IT. 



(tlands of mammals, and the abdominal sacks of the marsupials. 

 In some few cases also the male possesses similar organs, which 

 are wanting in the female, such as tlie receptacles for the 

 cva in certain male fishes, and those temporarily developed in 

 certain male frogs. The females of most bees are provided with 

 a special apparatus for collecting and carrying pollen, and their 

 ovipositor is modified into a sting for the defence of the larvsB 

 and the community. Many similar cases could be given, but 

 they do not here concern us. There are, however, other sexual 

 differences quite unconnected with the primary reproductive 

 organs, and it with is these that we are more especially concerned 

 — such as the greater size, strength, and pugnacity of the male, 

 his weapons of offence or means of defence against rivals, his 

 gaudy colouring and vai'ious ornaments, his power of song, and 

 other such characters. 



Besides the primary and secondary sexual differences, such as 

 the foregoing, the males and females of some animals differ in 

 structures related to different habits of life, and not at all, or 

 only indirectly, to the rerroductive functions. Thus the females 

 of certain flies (Culicidae and Tabanidse) are blood-suckers, 

 whilst the males, living on flowers, have mouths destitute of 

 mandibles.' The males of certain moths and of some crustaceans 

 (e. y. Tanais) have imperfect, closed mouths, and cannot feed. 

 The complemental males of certain Cirripedes live like epiphytic 

 plants either on the female or the hermaphrodite form, and are 

 destitute of a mouth and of prehensile limbs. In these cases it is 

 the male which has been modified, and has lost certain important 

 organs, which the females possess. In other eases it is the female 

 which has lost such jDarts ; for instance, the female glow-worm is 

 destitute of wings, as also are many female moths, some of which 

 never leave their cocoons. Many female parasitic crustaceans 

 have lost their natatory legs. In some weevil-beetles (Curcu- 

 liouidffi) there is a great difference between the male and female 

 in the length of the rostrum or snout ; ^ but the meaning of this 

 and of many analogous differences, is not at all understood. 

 Differences of structure between the two sexes in relation to 

 different habits of life are generally confined to the lower 

 animals ; but with some few birds the beak of the male differs 

 from that of the female. In the Huia of New Zealand the 

 difference is wonderfully great, and we hear from Dr. Duller ^ 



' Westwood, ' Modern Class, of ^ Kirby and Spence, ' Introduc- 



Inseots,' vol. ii. 1840, p. 541. For tion to Entomology,' vol. iii. 1820, 



the stcitement abcmt Tanais, men- p. 309. 



tioned below, I .am indebted to Fritz ' 'Birds of Xew Zealand,' '^va, 



Miiller. p. 66. 



