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TEXT-BOOK OF ENTOMOLOGY 



a few minutes of rest, and finally another coating is spun in the interior, when 

 the cocoon is all finished and completely air tight. The fibre diminishes in 

 thickness as the completion of the cocoon advances, so that the last internal 

 coating is not half so thick and so strong as the outside ones." (Amer. Natu- 

 ralist, i, p. 86.) 



The mode of spinning the cocoon of an ichneumon (Microgaster) 

 parasitic on Philampelus has been well described by John P. Marshall, 

 as follows : 



The first appearance of the parasite is represented in Fig. 572, i. A warty 

 excrescence appears on the back of the caterpillar, which slowly emerges until 



FIG. 572. Microgaster larvae spinning their cocoons : a, enlarged view of 5. After Mur.*h:ill. 



it is seen to be a larva enclosed in a delicate transparent membrane, as repre- 

 sented in 2. This it soon succeeds in bursting, and, rising to its full length, 

 balances itself a moment as in 3, then, bending double, it ejects from its mouth 

 a glairy liquid, which instantly changes to silk, and fastens the posterior end to 

 the skin of the caterpillar, as shown in 4, side view. It now begins to spin its 

 cocoon by attaching a silken thread to the silky mass by which it had previously 

 fastened itself to the caterpillar, and forming a series of loops of uniform size, 

 first from right to left, and then back again from left to right, as represented in 

 the front view, 5, and better in the enlarged view, 5 , the arrow heads show- 

 ing the direction in which the head of the larva moved while forming the loops. 

 The ends of the series, numbered l, 2, 3, 4, are fastened to the edges of the 

 ventral side of the body, which thus serves as a measure of the width of the 

 cocoon, and also acts as a support for the frail fabric in the first stages of spin- 

 ning. After the larva has fastened the fabric as far up on its ventral surface as 

 it can, conveniently, it then begins to spin free, as shown in the side view, 6, 

 where it is represented as just completing the first half of its cocoon, which 



