Page:The Effect of External Influences upon Development.djvu/67

Rh not come to maturity; for the ovaries of flies are fully formed though very small when the insects escape from the pupa. In later experiments, when the flies were fed from the first with sugar and meat-juice, the eggs developed very rapidly in the ovaries, and the first deposit occurred as early as ten days after metamorphosis.

It therefore appears that however rich the food of the larvae of these flies may be, it is only sufficient to form the ovaries, and not to bring any part of the egg-cells to maturity; and this seems to be equally true of bees and ants. Rich food is necessary in the imago-stage if the egg-cells are to ripen; and this probably explains the fact that the worker bees and ants as a rule produce no eggs: for they have usually to work hard to provide themselves with food, while the queens are supplied with rich food even in the imago-stage. It does exceptionally happen that the workers take rich food and exhibit an increased metabolism; and then they too bring the germs in their few egg-tubes to maturity, and lay eggs. Possibly we may explain Wasmann's experiments in a similar manner. (Cf. E. Wasmann (S. J.), 'Parthenogenesis bei Ameisen durch künstliche Temperaturverhältnisse,' Biol. Centralbl. Bd. xi. No. 1, Febr. 1, 1891). He frequently observed the production of eggs by the worker ants of several species he examined when the temperature was artificially raised. Warmth increases and accelerates metabolism and consequently stimulates the appetite. Moreover the experiment affected different species in different degrees, and this can be explained by the supposition that the ovaries had degenerated in different degrees. When they contain no egg-tubes at all, as in the case of Tetramorium caespitum, even the richest nourishment is of no avail to cause the production of eggs.

NOTE XII (p. 39).

In my book on The Germ-Plasm, I have simply spoken of double or multiple determinants as the foundation of dimorphism or polymorphism in the idioplasm. I conceived