178 



The follicles vary in their outer covering accorcling to the tree 

 on -which the 'insects live. Those from the Thvja occiclentalis 

 are the most beautiful, especially Avhen recent. Those from 

 deciduous trees are generally covered with bits of twigs, and of 

 the petioles of leaves, arranged longitudinally. Those of the 

 males are much smaller than those of the females, have the 

 lower orifice more prolonged, forming a long, 

 nearly cylindrical neck, and are generally cov- 

 ered with bits of leaves, sticking out on all 

 sides. The larvaa carry about these follicles till 

 they have done eating, fasten them In' a few 

 threads to the branch or leaf when they wish 

 to rest ; and when they want to descend from 

 one limb to another, they let themselves and 

 their pods down. Hence they are commonly 

 called " drop-worms " in Philadelphia, and 

 sometimes " basket-worms." The larva has 

 ten prolegs ; but these are exceedingly short 

 and retractile, so as to expose only the coronet 

 of hooks with which they are furnished. The 

 true legs, on the contrary, are very robust, in- 

 creasing in size from the first to the third pair, 

 and united in pairs by enormously lamelliform coxse. The male 

 and female pupge are very different fi'om each other, in size, form 

 and structure ; that of the .male being much the smallest, pro- 

 vided with visible Aving cases, etc., and with a less prominent car- 

 ina on the top of the thorax. The male pupa forces itself half 

 way out of the cylindrical lower orifice of its follicles when about 

 to disclose the winged insect. I should have stated above that the 

 follicles have two openings ; one above, through Avhich the larva 

 protrudes its head and legs when feeding and moving about ; 

 and to the edge of this upper orifice it fastens the strong silken 

 loop, by which the pod is permanently fastened to a twig when 

 the insect has come to its growth. It then turns around in its 

 follicle, so as to have its head towards the lower orifice, and 



Fig. 28. 



