254 THE PRINCIPLES OF Part II. 



we confine the term " primary ' : to the reproductive 

 glands, it is scarcely possible to decide, as far as the 

 organs of prehension are concerned, which ought to 

 be called primary and which secondary. 



The female often differs from the male in having 

 organs for the nourishment or protection of her young, 

 as the mammary glands of mammals, and the ab- 

 dominal sacks of the marsupials. The male, also, in 

 some few cases differs from the female in possessing 

 analogous organs, as the receptacles for the ova pos- 

 sessed by the males of certain fishes, and those tem- 

 porarily developed in certain male frogs. Female bees 

 have a special apparatus for collecting and carrying 

 pollen, and their ovipositor is modified into a sting for 

 the defence of their larvae and the community. In the 

 females of many insects the ovipositor is modified in 

 the most complex manner for the safe placing of the 

 eggs. Numerous similar cases could be given, but they 

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

 sexual differences quite disconnected with the primary 

 organs with which 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 various orna- 

 ments, his power of song, and other such characters. 



Besides the foregoing primary and secondary sexual 

 differences, the male and female sometimes differ in 

 structures connected with different habits of life, and 

 not at all, or only indirectly, related to the reproductive 

 functions. Thus the females of certain flies (Culicidae 

 and Tabanidse) are blood-suckers, whilst the males live 

 on flowers and have their mouths destitute of man- 

 dibles. 1 The males alone of certain moths and of some 



* Westwood, 'Modern Class, of Insects,' vol. ii. 1840, p. 541. In 



