Distinctions of Scx.—The abdomen is com posed of segments. nine for the female and ten for the male, and contains the viscera, and the lateral spiracles by which air is admitted to the respiratory system. it is shorter in most butter flies than the hinder wings; and in most moths is tufted along the dorsal line and on the end. 1 he terminal segment has various appendages, and contains the sexual organs of both sexes. There is often a very striking difference in size, color, and form between the females. especially among the butterflies, where procreation may be the sole duty of the imago during its brief sum mer existence. In case there are several broods of butterflies in a season, each brood may have its characteristic *coloration. Our Ajax butterfly is three-brooded, and before the facts of its life history were known, each brood had been given a specific name. By artificially varying the tem perature or moisture, any or all the seasonal forms may be produced at will from one and the same laying of eggs. The males. which are usu
ally more gayly decorated than the females and exceed them in number, are continually in search, about the food-plants. of mates. who exert a far reaching attracting power. Collectors utilize this instinct: having caught a female they ex pose it in a cage and soon are likely to Lind several males flocking about it. Under certain circumstances eggs may be laid by an unferti lized female (for which see REPRODUCTION and PARTnENouENEstS). Adherents of the doctrine of sexual selection believe the female exercises a choice among these assembled suitors. selecting for her partner the best. according to the stand ard of the species, and so maintaining the high quality of the race. A single impregnation is sufficient, and the impregnated females soon begin to lay eggs. having accomplished which. they die, in the great majority of cases. the ex ceptions being those which are double-brooded. or (a very few) where the adults largely survive the winter.