Of how many segments is the abdomen composed? The first or basal segment is depressed, while the others are more or less compressed. The _spiracles_ are, as in the locust, situated on the lateral aspects of the abdominal segments. What segments bear spiracles? The terminal segments of the abdomen differ in the two species. In the female the dorsal part of the (apparently) last segment is longer than the ventral part and is bent down over it forming a sort of hood over a space enclosed partly by this hood, partly by a bluntly-pointed projection from the ventral surface, and partly by the lateral margins of the segment. In this chamber lies the opening from which the eggs issue. In the male there are several backward-projecting, horny, thin processes. [Illustration: FIG. 43.--Wings of monarch butterfly, _Anosia plexippus_, to show venation; _c_, costal vein; _sc_, sub-costal vein; _r_, radial vein; _cu_, cubital vein; _a_, anal veins. In addition most insects have a vein lying between the sub-costal and radial veins called the median vein.] Make a drawing of the lateral aspect of the whole body. =Life-history and habits.=--The tiny, conical, yellowish-green eggs of the monarch butterfly are deposited on the under side of the leaves of milkweeds (_Asclepias_) and when examined under the microscope are seen to be very beautiful little objects finely ribbed with longitudinal and transverse striæ. The eggs are laid in April and May (depending on the latitude and season) by females which have hibernated in the adult condition. From the eggs the minute, cylindrical, pale-green, black-headed larvæ hatch in four or five days. As soon as hatched the larva devours the eggshell from which it has escaped and then feeds voraciously on the milkweed leaves. It grows rapidly, and in three or four days a blackish band or ring appears on each segment, and for the rest of its life it is very conspicuously colored with its black rings on a yellowish-green background. It molts three times, and in from twelve to twenty days is ready to pupate, or change to a chrysalis. When ready to pupate the larva usually leaves the milkweed plant, and seeks some such protected place as the under side of a fence-rail or jutting rock. Here it attaches its posterior extremity by a small silken web to the rail or rock, and casting its larval skin appears as a beautiful pale-green chrysalis with ivory black and golden spots. It hangs motionless, and of course without taking food, for from a week to two weeks (according to season and temperature), when the pupal cuticle breaks and the great red-brown butterfly (fig. 165) issues.