246 THE PRINCIPLES OF [Part II. 



are commonly ranked as primary, such as the complex ap- 

 pendages at the apex of the abdomen in male insects. 

 Unless indeed we confine the term " primary " to the re- 

 productive 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 or- 

 gans for the nourishment or protection of her young, as 

 the mammary glands of mammals, and the abdominal 

 sacks of the marsupials. The male, also, in some few 

 cases differs from the female in possessing analogous or- 

 gans, as the receptacles for the ova possessed by the 

 males of certain fishes, and those temporarily developed 

 in certain male frogs. Female bees have a special appa- 

 ratus for collecting and carrying pollen, and their oviposi- 

 tor 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 pug- 

 nacity of the male, his weapons of offence or means of 

 defence against rivals, his gaudy coloring and various 

 ornaments, his power of song, and other such charac- 

 ters. 



Besides the foregoing primary and secondary sexual 

 differences, the male and female sometimes differ in struct- 

 ures 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 Tabanidas) 

 are blood-suckers, while the males live on flowers and 

 have their mouths destitute of mandibles. 1 The males 



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



