THE SEXES, AND CRITICISM OF SEXUAL SELECTION. 2 1 



level of amphibians at least the females are generally the larger. 

 'J'his 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 

 (fi) the relatively large female cell or egg with the microscopic 

 male cell or spermatozoon. 



Figure of the Temale Ronellia (from Atlas of Naples Aquarium), 

 with its parasitic pigmy male enlarged. 



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 incubation and pregnancy. Further- 

 more, we must recognise the strengthening influence of the 



