THE BURNET ICHNEUMON. 293 



of Burnet Ichneumons proceeded from the body of a caterpillar 

 belonging to the geometridas. It was too much shriveled for 

 identification, but it was about as large as the larva of the swallow- 

 tailed moth. 



In the body of the caterpillar they live until the larval stage 

 is nearly completed, and then they burst on all sides through the 

 skin of their victim, proceed to a small twig, and there weave a 

 number of cocoons. These cocoons are about the eighth of an 

 inch in length, cylindrical in shape, set closely side by side and 

 fastened firmly together, so as to form a flattish mass extremely 

 variable in shape and size, the latter depending on the number 

 of cocoons. One of these masses now before me consists of one 

 hundred and seventeen cocoons, and its shape is that of a segment 

 of a circle, fixed to the twig by the fiat side. 



The ends of the cocoons are both closed, but when the young 

 ichneumon is hatched it makes its exit by cutting a circular flap 

 from one end of the cocoon, pushing the flap outward and then 

 creeping into the air. The insects are quite indifferent as to the 

 end of the cocoon through which they escape, and in the example 

 before me nearly two thirds of the creatures have escaped out of 

 one end and the remaining third out of the other. 



The texture of these cocoons is very firm and stiff, and the silk- 

 en material is so closely fitted together as to be completely water- 

 proof. The microscope shows that the exterior of the cocoon is 

 composed of white silken fibres matted tightly together, and rath- 

 er rough, while the inside of the circular flap shows that the in- 

 terior of each cocoon is smooth, hard, and of a pale yellow hue. 



The longest and largest cells occupy the centre of the mass, 

 while those at either end are shorter, smaller, and fewer, being 

 about one fifth of the entire number. Knowing the customs of 

 most hymenopterous insects, we may conclude that the females 

 occupy the centre and the males the extremities. 



There is a very remarkable pensile cocoon constructed by the 

 larva of another hymenopterous insect belonging to the same 

 family as the Burnet Ichneumon, and placed in the genus Cryptus. 



The insects of this genus seem to construct a strange variety 

 of cocoons, some being white, some yellow, and some banded and 

 mottled with black. The most remarkable forms, however, are 

 those in which the cocoon is attached to a thread some inches in 

 length, the other end of which is fastened to a bough or a leaf. 



