GROWTH AND REPRODUCTION. 211 



division of infusorians. In other words, the maximum size is rapidly- 

 reached when 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 favorable 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 anabolic preponderance. 



In regard to a common infusorian i^Lcucophrys patula), Maupas 

 observes that with abundant food the ordinary fission continues, but 

 with scanty nutrition a metamorphosis occurs, followed by six succes- 

 sive divisions, which have for their end conjugation. That is to say, 

 we have positive proof that in these lowest organisms, katabolic condi- 

 tions determine the beginning of sexual reproduction, a matter of no 

 small importance to the evolutionist. Generalizing, M. Maupas 

 concluded, that the reproductive power of ciliated infusorians depends, 

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

 (3) on the alimentary adaptation of the buccal organs. He also demon- 

 strates 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 reproduction, we 

 again reach the general conclusion that anabolic conditions favor 

 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 abun- 

 dantly 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 planarians went on apace when the food 

 supply was copious (anabolic condition), but if the amount of food 

 was reduced or altogether withdrawn (katabolic condition) the asexual 

 reproduction completely ceased. Bergendal reports that in the 

 transverse division of another planarian worm (Bipalhini), the severed 

 links were all sexually immature ; and the results of Rywosch demon- 

 strate the same antithesis between the sexual and the asexual process. 



