18 



THE EVOLUTION OF SEX. 



It would be unfair to argue from such an extreme case as that of 

 Bonellia alone, but there is no doubt that up to the level of 

 amphibians at least the females are generally the larger. This, then, 

 must be taken in connection with the conclusion of the previous 

 paragraph. A sluggish conservative habit of body tends to an 

 increase of size; lavish expenditure of energy keeps down the 

 accumulation of storage. Corroborative evidence will be afterwards 

 forthcoming, as we contrast (a) the large and small spores which mark 

 the beginnings of sex -differences, or (b) the relatively large female cell 



or egg with the microscopic male cell 

 or spermatozoon. 



Apparent exceptions occur, it is 

 true, among the higher animals. In 

 birds and mammals the males are 

 usually rather larger than the females. 

 This difference consists especially in 

 larger bones and muscles. The 

 apparent exception is in part the 

 natural result of the increased stress 

 of external activities which are thrown 

 upon the shoulders of the males when 

 their mates are incapacitated by incu- 

 bation and pregnancy. Furthermore, 

 we must recognize the strengthening 

 influence ot the combafs between 

 males, and the effect produced on 

 the accumulative constitution of the 

 females by the increased maternal 

 sacrifice characteristic of the highest 

 animals. 



While it is easy to point to the 

 general physiological import of large size and the reverse, physiology 

 is not yet far enough advanced to afford firm foothold in dealing with 

 the details of secondary sexual characters. It is only possible to point 

 out the path which will eventually lead us to their complete rationale. 

 This path will appear less vague if reverted to after some of the 

 succeeding chapters have been grasped. The point of view is simple 

 enough. The agility of males is not a special adaptation to enable 

 that sex to exercise its functions with relation to the other, but is a 

 natural characteristic of the constitutional activity of maleness; and the 

 small size of many male fishes is not an advantage at all, but simply 

 again the result of the contrast between the more vegetative growth of 

 the female and the costly activity of the male. So, brilliancy of color, 



Fig. io. — Figure of the female Bonellia (from 



Atlas of Naples Aquarium), with its parasitic 



pigmy male enlarged. 



IV. Other Characters.- 



