THE LEPIDOPTERA. 75 



as that of an ordinary kid glove, and so strong that it 

 is impossible to tear it, or indeed to cut it, except with 

 sharp instruments. The size of the case when the cater- 

 pillar is mature varies considerably, ranging from 25 to 30 

 lines or more in length, and about three in diameter, the 

 widest portion being a little behind the anterior aperture 

 (see Fig. ib). 



During the day the larva closes the entrance and spins 

 a loop of very strong silk over a twig, the ends being 

 joined to the upper edges of the case on each side ; in 

 this way it hangs suspended, the caterpillar lying snugly 

 within. I have often known a larva to remain thus for 

 over three weeks without moving, and afterwards resume 

 feeding as before ; this probably occurs while the inmate 

 is engaged in changing its skin. At night the larvae 

 may be seen busily engaged : they project the head 

 and first four segments of the body beyond the case, 

 and walk about with considerable rapidity, often lower- 

 ing themselves by means of silken threads ; the only 

 locomotive organs are, of course, their strong thoracic 

 legs, which appear to easily fulfil their double function of 

 moving both larva and case. If disturbed, these insects at 

 once retreat into their cases closing the anterior aperture 

 with a silken cord which is kept in readiness for the pur- 

 pose, and pulled from the inside by the retreating larva. 

 This operation is most rapidly performed, as the upper 

 edges of the case are flexible, and thus fold closely together, 

 completely obstructing the entrance. When full fed, this 

 caterpillar fastens its case to a branch with a loop of strong 

 silk, which is drawn very tight, preventing the case from 

 swinging when the plant is moved by the wind, and also 

 rendering the insect's habitation more inconspicuous, by 

 causing it to resemble a broken twig. The anterior aperture 

 is completely closed, the loose edges being drawn together 

 and fastened like a bag. The posterior end of the case is 



