40 



In speaking of sex. let us bear iu miud that among both animals and 

 plants there may be three kinds of individuals: Dioecious sijecies, in which 

 the individuals are unisexual, either male or female ; monoecious, with 

 bisexual or hermaphrodite individuals ; and parthenogenetic, in which in- 

 dividuals pi'oduce eggs that develop without fecundation. We may now take 

 up the question, vvliether the sex of the individual is determined by fac- 

 tors of the environment, or is it predetermined in the chromatin of the 

 sex cells, i. e., in either sperm or egg or both? Of the environmental fac- 

 tors, that which is supposed to play the most important role is nutrition, 

 and in the case of plants, it is probably the only one that need be consid- 

 ered, for other important factors, such as light and heat, are only influ- 

 ential in so far as they affect nutrition. But we should also understand 

 that we have two sorts or two categories of environmental conditions. In 

 case the fecundated egg develops wholly apart from the parental body, and 

 as a completely independent individual, its supply of nourishment is from 

 the external world ; but in those cases iu which the incubation of the fer- 

 tilized egg and the early development of the embyro take place within the 

 parental body, the food supply will depend upon the condition of the par- 

 ent. AVhile the conditions of these two categories seem very different, yet 

 it will be found that the final results are essentially the same. 



For the sake of simplicity, a few instances from the animal kingdom 

 will be mentioned. Experiments were carried on by Riley and others to 

 determine whether the starring of caterpillars of butterfles might influence 

 the number of males and females . for under normal conditions of nutri- 

 tion the catei-pillars produce both juales and females, and because it is not 

 possible, says Kiley, to make caterpillars take more food than they do nat- 

 urally. The results of the ex])eriments showed that an excess or diminu- 

 tion of food does not alter the proportion of the sexes. Upon this point 

 Morgan (Exp. Zool., p. 377) makes the following statement: "The futility 

 of many of these experiments has now become apparent, since it has been 

 shown that the sex of the caterpillar is already determined when it leaves 

 the egg. Under these circumstances it is not probable that feeding could 

 produce a change in the sex. It is much more probable that starvation or 

 overfeeding could only affect the proportion of males and females by bring- 

 ing about a greater mortality of the individuals of one sex." Numerous 

 studies have been made ui)on the silk worm by Kellog and Bell, and by 

 Cuneot upon flies and moths, to determine the influence of food conditions 

 upon the sex of the individual and upon that of the egg and sperm, with 



