236 THE EVOLUTION OF SEX. 



In Other words, abundant food is associated with asexual repro- 

 duction ; a check to the nutrition brings about the sexual process. 

 Maupas gives a vivid numerical statement of the stimulus to 

 reproduction by a sudden check to the nutrition. Leucophrys 

 at a temperature of 20° C, in richly nutritive conditions, will 

 give rise to sixteen thousand three hundred and eighty-four 

 individuals in three days ; but if the food be then suppressed, 

 this large number will in a few hours be multiplied by sixty -four, 

 resulting in a total of one million forty-eight thousand five 

 hundred and seventy-six individuals ! 



From cases already cited, which may be multiplied by con- 

 sulting Semper's "Animal Life," supplemented by a summary 

 of more recent researches by one of ourselves, the general con- 

 clusions may be drawn, — {a) That heat increases reproduction, 

 either directly or as the result of a preliminary acceleration of 

 growth ; {b) That increased food will, of course, favour growth, 

 but reproduction may follow all the more markedly as an 

 exaggerated nemesis; {c) That checks to nutrition, especially 

 in the form of sudden scarcity, will favour sexual reproduction. 

 The clearest result of all is, that a sudden katabolic change 

 favours reproduction, especially in its sexual form. Anabolic 

 conditions favour reproduction indirectly; the reverse condi- 

 tions have a direct influence ; in both cases, reproduction is the 

 expression of a katabolic crisis. 



7. Conclusion. — Primitively, then, reproduction was a kata- 

 bolic rupture of a mass of protoplasm. This becomes more 

 definite in cell-division of various kinds,, tending ever to occur 

 at the limit of growth when waste has made up on repair, or in 

 katabolic conditions due to the environment. In multicellular 

 animals, anabolic conditions favour overgrowth ; a check to this 

 brings about discontinuous asexual reproduction. With in- 

 creasing differentiation, the asexual multiplication is replaced by 

 the liberation of special sex-cells, by which the life-saving and 

 life-continuing sacrifice is rendered less costly. Just as asexual 

 reproduction occurs at the limit of growth, so a check to the 

 asexual process is often seen to involve the appearance of the 

 sexual, which is thus still further associated with katabolic pre- 

 ponderance. This is confirmed by the contrasts observed in 

 alternation of generations, where the two processes in varying 

 degrees of distinctness persist in the life-history of the same 

 organism. Corroboration is again afforded by the association 

 of sexual reproduction with sundry environmental checks of a 



