3. That this predisposition is: a. Weaker at first, before it builds up much of a body and gland system to fix it; b. Increasingly stronger as the new body becomes organized and developed; c. Liable to partial or complete upset in the very early stages; d. Probably quantitative--stronger in some cases than in others. The new definition is, then, really a combination and amplification of the three older points of view. The term "sex determination" does not mean to the biologist the changing or determining of the sex at will on the part of the experimenter. This might be done by what is known as "selective fertilization" artificially with only the kind of sperm (X or Y as to chromosomes) which would produce the desired result. There is as yet no way to thus select the sperm of higher animals. It has been authoritatively claimed that feeding with certain chemicals, and other methods to be discussed later, has affected the sex of offspring. These experiments (and controversies) need not detain us, since they are not applicable to the human species. Let us consider this fertilized egg--the contributions of the father and the mother. The total length of the spermatozoon is only about 1/300 of an inch, and 4/5 of this is the tail. This tail does not enter the egg, and has no other known function than that of a propeller. Its movement has been studied and found to be about 1/8 of an inch per minute. Only the head and neck enter the egg. This head consists almost entirely of the nuclear material which is supposed to determine the characters of the future individual. The ovum or egg contributed by the mother is much larger--nearly round in shape and about 1/120 of an inch in diameter. Besides its nucleus, it contains a considerable amount of what used to be considered as "stored nutritive material" for the early development of the individual. In ancient times the female was quite commonly supposed to be a mere medium of development for the male seed. Thus the Laws of Manu stated that woman was the soil in which the male seed was planted. In the Greek _Eumenides_, Orestes' mother did not generate him, but only received and nursed the germ. These quaint ideas of course originated merely from observation of the fact that the woman carries the young until birth, and must not lead us to imagine that the ancients actually separated the germ and somatic cells in their thinking.