Page:Popular Science Monthly Volume 15.djvu/489

 of attention to each larva, rearing them all into perfect insects—a benefit also accruing to the earlier hatched larvæ themselves, as they sooner reach maturity, and can thus obtain an abundance of food without rivalry. These earlier produced neuters have their reproductive systems only slightly less developed than egg-bearing insects; but natural selection, acting on the nurse, will cause them to grow less and less. Reproductive organs that do not produce are of no use to their possessors; and, as this slightly less developed but useless reproductive system would require more attention and more food from the fertile nurse than would those larvæ in which it was a mere rudiment, natural selection, by working on the instinct of the nurses, would modify, alter, or even suppress what was of no use. Or we may suppose that in the distribution of food to the larvæ the action is direct, some receiving such a minimum quantity of food that the reproductive organs remain rudimentary from want of material to build them up.

The necessity of producing offspring quickly in early spring would give rise to the instinct to feed the first produced brood of larvas on food insufficient in quality, or in quantity, or in both. The eggs, then, first laid by the female would develop into neuters. Neuters being sterile females, they would inherit the instincts of true females when they in turn took charge of the young. Whatever may be the worth of this theory, it throws some light on the curious fact that with some insects, as the bees and ants, the sexes are produced at different times. With bees the queen first lays eggs which produce neuters; then, at a later period, eggs producing males. According to Gould, the female of the Formica sanguinea—the red ant—lays eggs which will produce females, males, and workers at three different periods. That the habit is so is well known; but on the theory here supported can not we see how the habit arose, and the reason why such a habit exists?

Thus far food alone has been supposed to affect the development of insects, but there are several secondary factors; size of cell being one. Thus with the bee, the cell in which the queen is hatched is larger, differently formed, and in weight said to be equivalent to one hundred ordinary cells; the cells from which emerge the males are also larger than the cells of neuters. Now, the extra labor necessary to produce these cells in founding a new colony, the extra labor in attending to the inmates, and the non-necessity of having males or females at this early stage of colonial existence, are other reasons why the first-laid eggs produce only neuters. At present and in this place these points can be only touched on; in the future they will receive more elaboration.

If neuters have arisen in the manner suggested, how has their inflexibility of character been maintained? By natural selection modifying the instincts of the nurse. What at first arose through the incapability of one or several insects taking care of many insects, became through the action of natural selection, by the survival of those