Page:Popular Science Monthly Volume 64.djvu/104

100 by Lowne that individuals from the large maggots that have been well nourished are nearly always females, while those from small maggots, poorly nourished, are usually males. Cuénot first determined, in the three genera used in his experiments, that normally the number of males and of females is about the same. The results of his experiments, in which the maggots were well fed, were as follows—in Lucilia cæsar 49.27 per cent, of females; in Calliphora vomitoria 51.02 per cent, of females; and in Sarcophaga carnaria 51.62 per cent, of females. It is obvious that the presence of an abundance of food did not produce an excess of females. In another experiment in which the maggots received as small a quantity of food as possible there was great mortality and the pupæ were of diminutive size. The results were as follows—Lucilia cæsar 57.92 per cent, of females; Calliphora vomitoria 57.92 per cent, of females; and Curtonerva pabulorum 26 females and 17 males. It is even more evident from the results of this experiment that starving does not have the effect of producing an increase in the number of males. Several variations of these experiments were made, but the results were always the same. Cuénot also tried to find out if the amount of food taken by the individual during its growth has any effect on the kinds of eggs that are produced. The larvæ of Calliphora vomitoria were starved from their birth until they pupated. They gave rise to twelve males and five females, whose size was scarcely half that of the normal individuals. These dwarf flies, confined in a cage with sweetened water and meat, laid twenty times. The larvæ that hatched were kept in a well-nourished condition, and gave rise to 359 females and 353 males. The results show that the amount of food supplied to the young maggots had no effect upon the relative number of male and female eggs that they produced. It is true that these animals, when poorly nourished, gave rise to only a few eggs, but the relative number of eggs that became male or female remained the same.

Among the earliest experiments that were carried out to show whether the sex of the individual could be determined by external conditions were those of Born in 1881, and of Yung in 1883 and 1885. Born tried to show that more male frogs develop when the fluid containing the fertilizing spermatozoa is more concentrated, but this conclusion has been shown to be wrong. Born also fed the tadpoles of Rana temporaria on a rich diet consisting of water plants and of the flesh of frogs and of tadpoles. A large percentage of females developed which Born attributed to the abundance of food. It was shown, however, by Pflüger in the following year, 1882, that Born's conclusion was erroneous, because, even under normal conditions, female frogs are more numerous. Pflüger found that the normal proportions of females to males is often as high as five to one; and this corresponds also to the