From the facts elaborated by our guides in this matter, it would seem that the female is the primary unit of creation, and that the male functions are simply supplemental or complementary. Parthenogenesis among many of the lower forms of life would seem to favour this view. We are given to understand that under conditions favouring katabolism, the males among Rotifera wear themselves out, under which conditions the females become katabolic enough to do without them.
Among the common Rotifera, the males are almost always very different from the females, and much smaller. Sometimes they seem to have dwindled out of existence altogether, for only the females are known. In other cases, though present, they entirely fail to accomplish their proper function of fertilization, and, as parthenogenesis obtains, are not only minute, but useless.[24]
So long as food is plentiful, the females continue to raise parthenogenetic offspring, but with the advent of hard times, when food is scarce or of a poor quality, the parthenogenetic series is interrupted by the appearance of males. Although, unaided by the male, the female of certain species is able to reproduce, he has never been able to propagate without her co-operation.
Concerning the conditions which underlie the production of females and males we have the following from The Evolution of Sex, by Geddes and Thomson:
Such conditions as deficient or abnormal food, high temperature, deficient light, moisture, and the like, are obviously such as would tend to induce a preponderance of waste over repair—a katabolic habit of body,—and these conditions tend to result in the production of males. Similarly, the opposed set of factors, such as abundant and rich nutrition, abundant light and moisture, favour constructive processes, i.e., make for an anabolic habit, and these conditions result in the production of females.[25]
Among the lower orders of animal life, notably insects, we are assured that an excess of females denotes an excess of formative force, and that an excess of males indicates a deficiency on the part of the parents. In the case of bees, the queen, which is the highest development, is produced only under the best circumstances of nutrition, while the birth of the drone, which is the lowest result of propagation, is preceded by extremely low conditions.
The working bee which, being an imperfect female, may not be impregnated, will, however, give birth to parthenogenetic offspring, such offspring always being male. In the case of Aphides, the sex depends on the conditions of nutrition. During the summer months while food is plentiful and nutritious, females are parthenogenetically produced, but with the return of autumn and the attendant scarcity of food, together with the low temperature, only males are brought forth. In seasons in which food is abundant, Cladocera and Aphides lose the power to copulate; they nevertheless multiply parthenogenetically at a marvellous rate of increase,
giving birth to generation after generation of parthenogenetic females, so long as the environment remains favourable, but giving birth, as soon as the conditions of life become less favourable, to males and to females which require fertilization.[26]
It is stated also that if caterpillars are shut up and starved before entering the chrysalis stage, the butterflies which make their appearance are males, while the highly nourished caterpillars are sure to come out females. In the case of moths unnutritious food produces only males.
Experiments show that when tadpoles are left to themselves the average number of females is about fifty-seven in the hundred, but that under favourable conditions the percentage of females is greatly increased. The following is the result of one series of observations by Yung. In the first brood, by feeding one set with beef, the percentage of females was raised from fifty-four to seventy-eight; in the second, with fish, the percentage rose from sixty-one to eighty-one, which in the third set, when the nutritious flesh of frogs was supplied, only eight males were produced to ninety-two females.[27]