TWO KINDS OF GERM-CELLS 495 



The theory that the presence of one X-element in a fer- 

 tilised ovum means male offspring, and that the presence of two 

 means female offspring, is morphological, and our physiological 

 sense is left unsatisfied. Is the difference significant in itself, 

 or as an index of metabolic differences ? If the eggs with more 

 chromatin than their neighbours develop into females, and if 

 chromatin be an index of a relatively preponderant anabolism or 

 anabolic capacity, can the theory be brought into line with the 

 thesis of The Evolution of Sex, that the female is the outcome 

 and expression of relatively preponderant anabolism, and the 

 male of relatively preponderant katabolism ? 



Baltzer has observed that about half of the eggs of the sea- 

 urchin are distinguished from the others by having one of the 

 eighteen chromosomes represented by a short " hook-chromo- 

 some " instead of a normal " rod-chromosome," and there is 

 indirect evidence that those ova with the short " hook-chromo- 

 some " become males. In discussing this case and comparing 

 it with the state of affairs in the various insects already referred 

 to, Boveri points out that in both cases the fertilised ovum from 

 which a female develops has more chromatin than that from which a 

 male develops, and that the amount of chromatin has a regulative 

 influence on the amount of cytoplasm. He recalls cases, such 

 as Issakowitsch's Daphnids, von Malsen's Dinophilus, and 

 Russo's rabbits, where it appears to him proved that nurtural 

 conditions influence sex-determination. The better-equipped 

 ova become females. He suggests, therefore, that in some cases 

 nurtural influence operates variably or unequally on sexually 

 indifferent germ-cells, giving them a bias to the one sex or the 

 other, and that in other cases the decision is due to an internal 

 factor such as the presence of stronger " assimilation-chromo- 

 somes " in some of the ova. 



On the other hand, it may be that the additional chromatin 

 material is of qualitative importance. Thus, to give point to 

 his theory, Prof. E. B. Wilson suggests quite provisionally 



