2 25 THE EVOLUTION OF SEX. 



]^Iaupas, and others, have shown that abundant nutrition favours 

 the asexual multipHcation, i.e.^ the division of infusorians. In 

 other words, the maximum size is rapidly reached ^Yhen food 

 is abundant, but the conditions at the limit of growth bring 

 about reproduction. Preponderant anabolism leads up to the 

 possibility of multiplication, but we need the onset of katabolism 

 to bring about the reproductive crisis. Gruber also notes, that 

 in the very reverse of favourable conditions, rapid division with 

 diminution of size and resulting conjugation sets in; and 

 Khawkine observes the occurrence of division, both at an 

 optimum and in famine. In both cases a katabolic crisis is 

 associated with reproduction, though the crisis may be, and 

 often is, preceded by an anabohc preponderance. 



In regard to a common infusorian {Leucophrys patula), 

 Maupas observes that with abundant food the ordinary 

 fission continues, but with scanty nutrition a metamorphosis 

 occurs, followed by six successive divisions, which have for 

 their end conjugation. That is to say, we have positive proof 

 that in these lowest organisms, katabolic conditions determine 

 the beginning of sexual reproduction, a matter of no small 

 importance to the evolutionist. Generalising, M. Maupas 

 concludes, that the reproductive power of ciliated infusorians 

 depends, (i) on the quality and quantity of the food; (2) on 

 the temperature; (3) on the ahmentary adaptation of the 

 buccal organs. He also demonstrates, that with a vegetarian 

 diet their rate of asexual reproduction is much less, and the 

 size smaller. Taking these facts, along with his important 

 demonstration that the life of ciliated infusorians runs in cycles 

 of asexual reproduction, necessarily interrupted (if the life of 

 the species is to continue) by conjugation or sexual repro- 

 duction, we again reach the general conclusion, that anabohc 

 conditions favour asexual reproduction, rather than sexual ; and 

 that while preponderant anabolism is the necessary condition 

 of the overgrowth which makes the asexual reproduction 

 possible, the onset of katabolic preponderance is necessary to 

 the act itself. 



Semper quotes an interesting observation by Strethill Wright, 

 unfortunately somewhat vague, that certain polyps multiply 

 abundantly in the dark by buds, while in the light, and with 

 insufficient supplies of food, they bring forth sexual individuals 

 or medusae. !More precise is the fact already cited from 

 Zacharias, that the spontaneous asexual multiplication of 



