Influence of Eiivironment upon the Organism. 453 



Copious nutrition is well known to favour not only increase 

 in size, but asexual reproduction, which is only a process of 

 more or less continuous growth. With abundant nutrition a 

 plant may go on reproducing asexually by stolons, etc.; if the 

 nutrition be checked in root pruning, etc., sexual reproduction 

 is incited. That scarcity of nutrition is one of the conditions 

 of the change from parthenogenesis to sexual reproduction in 

 Aphides is probable; and Keller (91) has recently shown 

 that stoppage of nutrition in Phylloxera causes the partheno- 

 genesis to cease. Good nutrition, ovarian, uterine, or larval, 

 tends to the production of female, rather than of male forms. 

 It is the peripheral and better nourished cells in the alveoli 

 of the hermaphrodite glands of snails which form ova (100), 

 while those more central become spermatogonia. Wilckens 

 and others (107, 83) conclude that better maternal and em- 

 bryonic nutrition tends to female offspring. Mace (95) 

 observes that the embryos of Ascaris dactyluris, developing in 

 anabolic conditions within the mother, were all females. 

 Yung (108) greatly increased the proportion of female tad- 

 poles, by increasing the quantity and quality of the food. 

 Kich nutritive environment may apparently replace the 

 necessity of male stimulus (90, 106). In a wider connection, 

 Sutton, in his suggestive "General Pathology" and else- 

 where (104, 105), has laid great stress on the importance of 

 hypertrophy in evolution, believing that it is the principal pro- 

 cess in the transition from hermaphroditism to unisexuality. 

 Scarcity of food has been shown to have opposite effects to 

 those above stated in regard to abundance ; tending to reduc- 

 tion of size, to sexual not asexual reproduction, to the 

 production of males rather than of females. Zacharias (110) 

 has made the interesting observation, that with abundant 

 nutrition a certain Planarian went on reproducing asexually, 

 while checking the nutrition stopped the process. In abun- 

 dant nutrition Infusorians go on reproducing rapidly by 

 fission ; with less luxurious diet the rate is decreased ; at 

 low ebb they conjugate (96, 97, 98, 86). To Kolph (101a), 

 and others, conjugation has seemed almost identical with 

 the satisfaction of hunger. Eeduction of nutrition appears 

 to be a condition necessary for the conjugation of the spores 



