220 



they were the same kind of moths. As This is accomplished as follows : The 



in Cecropia the male moths are some- larva grasps firmly the branch with its 



what smaller than the females, and the posterior legs ; reaches out a considerable 



antennae show the same kind of differ- distance along the petiole, and bites it 



ences, i. e., the antennae of the males are through in several places. This causes 



much larger and feather-like. In color, the leaf to droop ; the larva now reaches 



the sexes of Cecropia are much alike, but out, seizes the drooping leaf, and draws it 



in this moth the differences in color are within convenient reach, where it can be 



very great, the dominant color in the fe- eaten at leisure. This is a wonderful dis- 



male being a reddish brown, while that in play of instinct, yet it is not infallible, be- 



the male is a very dark-bfown or almost cause at times the petioles are eaten too 



black. Thus these moths furnish an ex- far through, and when they droop, break 



cellent illustration of what is called sexual completely away and fall to the ground, 



dimorphism, a term used for thoseanimals When ready to spin its cocoon, the 



in which the sexes are very different in adult larva is about two inches long; 



appearance, a subject to which Charles these cocoons are very different from 



Darwin gave considerable attention, in those of Cecropia. As a rule, they are 



his "Descent of Man." found suspended from a branch by a silk- 



The female moth lays her cream-col- en cord, the length of which depends up- 



ored eggs, which are a little smaller than on the length of the petiole of the leaf in 



those of Cecropia, upon shrubs and trees which the cocoon was spun. Thus if the 



in clusters of five or six. The small larva leaf has only a short petiole, this cord is 



usually hatches in about ten days, and also short, but if the petiole is two or 



feeds upon the leaves of ash, sassafras, three inches long, the suspensory cord is 



lilac, tulip tree, maple, cherry, and a mum- correspondingly long. The larva in con- 



ber of other trees and shrubs, but it is structing its cocoon, first spins a strong 



much more select in the choice of its food band around a twig, and binds the petiole 



than Cecropia. The larvae have voracious of the leaf to the stem ; this band extends 



appetites, devour many leaves and grow down the petiole to the cocoon, and thus 



at a correspondingly rapid rate. The dif- anchors it. The cocoon proper, or the 



ferences between the very young and the part occupied by the chrysalis, is spun in 



adult larva, aside from that of size, are a folded leaf. When this leaf dies and 



very great. On account ofjthe very lim- rots away, the cocoon hangs freely sus- 



ited elasticity of the skin, this larva, like pended by the cord, but it is very evident 



other insect larvae, only increases in size that the cocoon has been moulded in a 



after shedding. This is periodically ac- leaf by the prints of the veins which re- 



complished by throwing off the old skin, main upon it. A valve-like opening oc- 



which prevented expansion, and by grow- curs in the upper end, through which the 



ing a new and larger one. Promethea moth emerges. . 



has from three to five of these moults, the The wings of the chrysalis are very 

 number being influenced apparently by small as compared with those of the adult 

 climate, since southern larvae have more moth ; are folded to the body on the under 

 moults than northern ones. The time be- side, and covered by the pupal skin. Dur- 

 tween these moults varies from two days ing the winter they remain transparent 

 to a week. since there are at this time none of the 

 The leaves upon which the larvae feed rich colors present which are later found 

 may have long or short petioles. A in the moth. About ten days before the 

 singular account has been given of how moth emerges the wings become white, 

 these larvae have overcome the difficul- a few days later definite colors begin to 

 ties associated with feeding upon long- appear on the under side of the wings 

 petioled leaves. There is considerable between the veins. While in the adult 

 risk of falling and of the leaf breaking moths the colors in the two sexes are 

 away when a large larva crawls out upon very distinct, at this time their wings are 

 a slender petiole. The larva avoids these verv similar. The wings do not long re- 

 risks and yet reaches the blade of the leaf, tain this similarity, but gradually be- 



