ToiiAcco-Tvona. PAnAsixE descmbeh. its HEAb. its Bony. 

 Uie worm, yet so sligliLly that they are liable to be detached by the slight- 

 est force, some of them falling off. sometimes, merely from the motions of 

 the worm. 



When these parasites issue from it the worm has become so weakened 

 and exhausted that it ceases feeding and moving about, and in about three 

 days afterwards all traces of its vitality have vanished. The multitude of 

 minute hooks with which the soles of its pro-legs are furni-^hed, however, 

 continue to hold the dead worm to the stalk of the plant, with its head 

 hanging downwarks and its body shrunken and flaccid from the evapora- 

 tion of its fluids, until some agitation of the plant by the winds or other 

 violence detaches it and it falls to the ground. 



In the meantime the parasites change to piipoa, and after remaining in 

 the cocoons seven days they come out from them iti their perfect form. The 

 flies are black, with clear transparent wings, and legs of a bright lawny 

 yellow color, the hue of bees-wax, with tho hind feet and the tips of the 

 hind shanks dusky. They belong to the order Hymenoptera, and to that 

 group of the Ichneumon-flies, which in works of science have been termed 

 IchneumonideH adscili or the family Bkaconid/e. Several of the species of 

 this family present the singular character of having the eyes pubescent, 

 numerous tine short erect hairs arising from their surface. These pertain 

 to a particular genus which has received the name Mia-ogaster, from two 

 Greek words, equivalent to our English term " small-i)ellied." It is to this 

 genus that these parasites of the Tobacco-worm belong. And they were 

 described by Mr. Say, in a posthumous paper which was published in the 

 year 1885, in the Boston Journal of Natural History, vol. i, p. 262, under 

 the name Microgaster congregata or the Congregated Microgaster, in allu- 

 sion to their young being ibund together in such numbers upon a single 

 worm. 



The ToBACco-woRM Parasite, Microgaster congregala, is of a coal black 

 color and 0.14 long when living. After death it contracts in drying and is 

 tVien scarcely 0.12 in length, and the male is a size smaller, not exceeding 

 0.10. Its head is spherioidal, or of a flattened globular form, with the an- 

 tennae inserted in the middle of the front side. The antcnnoe are coarse, 

 thread-like, and longer than the body in the male, shorter in the female. 

 They are composed of about seventeen joints so closely connected that their 

 articulations are difficult to perceive. The joints gradually become slightly 

 Shorter and less thick as they approach tho tips. The palpi and jaws are 

 white. The eyes are distant from each other on the sides of the head, and 

 in a strong I'ght their surface is seen to be closely bearded over with mi- 

 nute short hairs. Between them on the crown the eyelets or ocelli appear 

 as three small glassy dots placed at the corners of a triangle. The thorax 

 io the broadest part of the body. It is egg-shaped, its surface minutely 

 and closely punctured, and back of the middle it is crossed by a deep groove. 

 The abdomen is oblong oval, and about the same length as the thorax. It 

 is smooth and shining, except the two first segments which are rough from 

 obscure shallow punctures, with an elevated longitudinal line in the middle. 

 On its underside the three first segments are pale yellow, with a dusky 



