Page:Popular Science Monthly Volume 64.djvu/112

108 to the contrary, for in the great majority of forms all the spermatozoa that are formed develop in the same way and are, so far as we can see, capable of fertilizing the eggs.

Beard's conclusions in regard to the determination of sex may be summarized as follows:

1. The sex of the individual is determined in the egg before fertilization.

2. The determination of sex probably takes place at the time of the reduction in the number of chromosomes.

3. Each egg and its two polar bodies are potentially of the same sex, either male or female.

4. A corresponding differentiation of the primary germ-cells takes place in the male. An early separation of the spermatogonial cells into male and female occurs. After this each cell may continue to divide, but remains of the sex that it has acquired in the differentiating division. Finally each of these cells produces four spermatozoa. This division is comparable to the one in the egg-series when the polar bodies are given off, so that each group of four spermatozoa corresponds to a female egg and its three female polar bodies, or to a male egg and its three male polar bodies; but in the cases of the spermatozoa the individuals are supposed to be without sexual qualities. It is the egg alone that determines the sex.

5. One set of these fourfold groups of spermatozoa Beard supposes to have become functionless, in the sense that even if it develops the spermatozoa have lost the power to fertilize the eggs. The other spermatozoa are functional so far as fertilizing the egg is involved, but, as stated above, take no part in the determination of sex.

Beard also advances certain views in regard to parthenogenesis. The sex of the individual that develops from a non-fertilized; i. e., from a parthenogenetic egg, is not in any sense a consequence of the non-fertilization of the egg. Whether the individual is a male or a female depends entirely upon whether a male or a female egg has been produced. Whenever we find long series of parthenogenetic females, as in the aphids, developing from and also producing parthenogenetic eggs, Beard supposes that only female eggs have been produced in the ovary, and that the male eggs, which have appeared in one at least of the first generations of the germ-cells 'must be either delayed in their ripening or suppressed.' Here we meet with a paradox that is so