149 



except in the eighth stage, when they are found to have disap- 

 jjeared entirely. In the seventh moult the larva undergoes great 

 changes. The legs are no better developed after that change than 

 before it, though towards the latter part of the eighth stage each 

 of the true legs is found to be placed upon a distinct inammillary 

 projection of the segment ; but immediately after the seventh 

 moult the larva is found to have increased in thickness, till its 

 vertical thickness is more than one-third its width ; this thick- 

 ness continues to increase, and the width to decrease, till, before 

 shedding its last larval skin and disclosing the pupa, it has become 

 distinctly cylindrical. During this time and in the same gradual 

 way the head has become convex above, and deflexed, until the 

 tropin are no longer in the axis of the body, but have assumed 

 the position usual in ordinary caterpillars. During this stage it 

 eats nothing, and its body seems to be a mass of oil-globules, 

 which, however, have been increasing in number during the last 

 two stages. It lies quiescent in the part of the mine to which 

 it had retired before moulting, and seems disinclined even to 

 wriggle when touched. Pari passu with these external changes 

 internal changes as important have taken place. The spinneret 

 has made its appearance at the seventh moult, and the long 

 convoluted silk-glands may be seen lying along on each side of 

 the intestine. These organs are seen to much the best ad- 

 vantage in a larva of the cylindrical group under slight pressure. 

 The oil-globules arrange themselves along the median line of the 

 body, sending two branches out on each side, in each segment, 

 and gradually the form of the pupa becomes visible under the 

 thin larval integument. 



The mode of spinning the cocoon is as follows. The larva 

 having, as above stated, retired to a part of its mine, and cast 

 its skill, lies quiet for two or three hours. Up to this time the 

 mine is flat. Turning upon its back, and applying its spinneret 

 to the separated upper cuticle, it weaves short bands of silk in 

 a line. These, by their contraction, produce a narrow longitu- 

 dinal fold in the cuticle, thus drawing it tightly and raising it 

 above the lower surface, which is made to curve slightly ; the 

 mine has thus become tentiform. Turning again upon its ventral 

 surface, and slowly revolving around, it spins beneath it a circu- 



