hereditary:—I mean that the determination of sex may be dependent on the composition of the germ. The fact that many families consist chiefly either of male or of female children could hardly be accounted for in connection with any external influences. If, however, we conceive of the germ-plasm as composed of 'male' and 'female' ids, the numerical relations of these will usually be as 1:1. But deviations in this respect will occur, and may be increased by means of the processes of 'reducing division' and 'amphimixis'; and when a certain point has been reached they may lead to all or the majority of the children of the same parents being of one sex. I hope to treat of this matter in greater detail on another occasion.
The idea that sexual dimorphism is based on the presence of more or less markedly different 'male' and 'female' ids in the idioplasm, harmonizes very well with the occasional determination of sex by external influences. Just as the 'worker-ids' of the bee become active by the poor food-supply of the larva, while the 'queen-ids' remain inactive, it would seem to be possible that in the case of the frog abundant nourishment in the larval stage should usually lead to 'female' ids becoming active, while meagre feeding leads to a preponderance of 'male' activity. In like manner it is possible that in the case of the bee any factor that is connected with the act of fertilization might be the means of stimulating the female-ids to activity.
NOTE XIII (p. 43).
I am quite aware that pathological abnormalities occur in which entire parts or organs may be wanting. But such cases do not contradict the view of the phyletic nature of the process by which typical parts become rudimentary, to which I have given expression on p. 35. It is true that the brain may be partly or altogether wanting in a human embryo or may be abnormally small, or defects may occur in the heart, or larger or smaller regions of the limbs may be wanting;
