802 THE STUDY OF ANIMAL LIFE CHAP. 



fusorians and passive Gregarines, to the feverish birds 

 and sluggish reptiles, and down into the detailed contrasts 

 between order and order, species and species, an antithesis 

 may be read between predominant activity and pre- 

 ponderant passivity, between lavish expenditure of 

 energy and a habit of storing, between a relatively more 

 disruptive (katabolic) and a relatively more constructive 

 (anabolic) series of changes in the protoplasmic life of the 

 creature. The -contrast between the sexes is an expression 

 of this fundamental alternative of variation. 



The theory is confirmed by contrasting the character- 

 istic product of female life passive ova, with the char- 

 acteristic product of male life active spermatozoa ; or 

 by summing up the complex conditions (abundant food, 

 favourable temperature, and the like) which sometimes 

 favour the production of female offspring, with the 

 opposite conditions which sometimes favour maleness. 



The thesis of The Evolution of Sex (Geddes and Thom- 

 son, 1889) was that males and females differ in the 

 nature and intensity of their metabolism. They live at 

 different physiological rates, the expenditure of the male, 

 or the ratio of katabolism to anabolism, being rela- 

 tively greater than in the female. This view is in part 

 confirmed by the important experimental work of 

 Geoffrey Smith, who has shown how the parasitic Crusta- 

 cean Sacculina alters the metabolism of the male crab 

 and induces the production of ova and the putting on of 

 feminine characters. '' This adaptive regulation," he 

 says, ' consists in the production of at least a partially 

 female condition of metabolism as opposed to a wholly 

 male condition, the female condition being preponder- 

 antly anabolic or conservative, as opposed to the katabolic 

 male condition, and by this change from a katabolic to 

 a more anabolic condition the animal can withstand 

 better the drain on its system increased by the parasite." 

 Mr. Walter Heape, an accomplished embryologist, inclines 

 to the same view. Writing in 1913, he says : 



" The Male and the Female individual may be compared in 

 various ways with the spermatozoon and ovum. The Male is active 

 and roaming, he hunts for his partner and is an expender of energy ; 



