H 



THE EVOLUTION OF SEX. 



CHAPTER II. 



THE SEXES, AND CRITICISM OF SEXUAL SELECTION. 



I. To gain a firmer and broader foundation on which to base a 

 theory of the differences between the sexes, it is necessary to take 

 another review of the facts of the case. Instead of considering the 

 differences as they are expressed in the successive classes of animals, 

 it will be more convenient to arrange them for themselves, according 

 as they affect habit, size, length of life, and the like. The review 

 must again be merely representative, without any attempt at com- 

 pleteness. 



Fig. 5. — -Male and Female Coccus Insects. 



a, part of a cactus-plant with the excrescences due to 

 coccus insects; b, male; c, female. 



II. General Habit. — Let us begin with an extreme yet well 

 known case. The female cochineal-insect, laden with reserve prod- 

 ucts in the form of the well-known pigment, spends much of its life 

 like a mere quiescent gall on the cactus-plant. The male, on the other 

 hand, in his adult state is agile, restless, and short-lived. Now this 

 is no mere curiosity of the entomologist, but in reality a vivid emblem 

 of what is an average truth throughout the world of animals — the 

 preponderating passivity of the females, the predominant activity of 

 the males. These coccus insects are the martyrs of their respective 

 sexes. Take another illustration, again somewhat extreme. There is 

 a troublesome threadworm (Heterodcra schactii) infesting the turnip- 

 plant, which parallels in more ways than one the contrast of the coccus 

 insects. The adult male is agile, and like many another threadworm; 



