486 HEREDITY AND SEX 



Marchal and others in certain parasitic Hymenoptera, it seems 

 that one fertihsed egg may give rise to a chain of embryos, and 

 these are of the same sex. This again corroborates the view that 

 the sex may be absolutely determined in the eg^. 



Classification of Possible Factors. — Ingenuity has almost 

 exhausted itself in discovering possible factors in the deter- 

 mination of sex, and though the majority of the suggestions 

 offered cannot be taken seriously (and need not even be men- 

 tioned) there remain a number of factors which may be 

 reasonably considered. 



We may arrange these possible factors in three sets : — 



A. External Influences, such as nutrition and temperature, 

 operative on the parents, or on the liberated germ-cells, or on 

 the embryos, or even on the larval stages if there are such. 



B. Parental Influences, other than those directly traceable 

 to peculiarities of diet and the like : e.g. whether the parent is 

 young or old, strong or weakly ; whether the birth is a first or a 

 last ; whether one parent is much older than the other ; and so on. 



C. Internal Conditions in the gerrn-cells themselves : e.g. the 

 size of the ovum, the age of the ovum, the relative freshness or 

 staleness of the spermatozoa, the equality or inequality of the 

 number of chromosomes in the ovum and the sperm, the chances 

 of maturation divisions, the conditions of amphimixis itself. 



It may be useful also to classify the factors according to the 

 time at which the sex may be thought of as fixed. 



{a) It may be that a young and immature ovum has already 

 a constitutional predisposition towards becoming a male or a 

 female — that is (from our point of view) towards becoming a 

 sperm-producer or an egg-producer. It may be that this early 

 predisposition, which will apply also to the spermatozoa, is de- 

 pendent on nutritive conditions, directly affecting the cytoplasm 

 of the germ-cell, or the nucleoplasm, or both. Or it may be that 

 the young germ-ceUs fluctuate as regards the ratio of anabolism 

 and katabolism, and that they may be swayed by slight 



