204 THE DESCENT OF MAN. 



the nourishment or protection of her young, such as the mam- 

 mary glands of mammals, and the abdominal sacks of the marmi- 

 pials. In some few cases also the male possesses similar organs, 

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

 ova 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 defense of the larvas and 

 the community. Many similar cases could be given, but they do 

 not here concern us. There are, however, other sexual differ- 

 ences quite unconnected with the primary reproductive organs, 

 and it is with these that v/e are more especially concerned — such 

 as the greater size, strength, and pugnacity of the male, his 

 weapons of offense or means of defense against rivals, his gaudy 

 coloring and various 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 reproductive functions. Thus the females 

 of certain flies (Cullcidse 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. g. Tanals) 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 cases it is the fe- 

 male which has lost such parts; for instance, the female glow- 

 worm is destitute of wings, as also are manj' female moths, some 

 of which never leave their cocoons. Many female parasitic crus- 

 taceans have lost their natatory legs. In some weevil-beetles 

 (CurculionidEe) 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 under- 

 stood. Differences of structure between the two sexes in relation 

 to different habits of life are generally confined to the lower ani- 

 mals; but with some few birds the beak of the mr.le differs from 

 that of the female. In the Huia of New Zealand the difference is 

 wonderfully great, and we hear from Dr. Buller- that the male 

 uses his strong beak in chiselling the larvffi of insects out of de- 



1 Westwood, 'Modern Class, of Insects," vol. il. 1840, p. 541. For the 

 statement about Tanais, mentioned below, I am indebted to Fritz 

 MuHer. 



'^ Kirby and Spence, 'Introduction to Entomology,' vol. iii. 1S26, p. 309. 



» 'Birds of New Zealand,' 1872, p. 66. 



