444 INSECTS INJURIOUS TO VEGETATION. 



wards." His samples of diseased wheat-straw of the previous 

 year yielded him, in the spring, numerous specimens of the 

 Eiirytoma, and nothing else. A few specimens of the same 

 insect were developed from the tumors on plants of the present 

 season, thus showing that "a small proportion of the larvae 

 undergo their transformations during the summer." Among 

 his specimens he obtained a very few Hymenopterous insects, 

 differing from the Eurytoma, and probably parasites. In sev- 

 eral instances Professor Cabell saw a small semitransparent 

 whitish worm, scantily covered with hairs, in the same cell 

 with a lifeless joint-worm, and adhering to its body. In other 

 cases, the former kind of worm or larva "was found alone, but 

 it was then of a larger size, and there were almost always 

 some more or less unequivocal signs of the worm having fed 

 on the joint-worm." 



Having been favored by Professor Cabell with some sam- 

 ples of wheat-straw, containing living joint-worms, I have been 

 able to verify his observations during the present summer, 

 while this sheet is passing through the press. At my request, 

 Professor Jeffries Wyman, of Harvard College, an accomplished 

 anatomist, and a skilful microscopical observer, has examined 

 these larva?, and also some of the parasitical worms, found in 

 the straw, and has made for me several magnified sketches of 

 them. Both kinds are found to differ essentially from the 

 larvae of the locust and of the willow gall-flies, with living 

 specimens of which I have compared them. Their bodies are 

 softer, and their skins more delicate and tender; and the form 

 of the head and structure of the mouth are entirely unlike 

 those of the Cecidomyian larva;. The true joint-worm varies 

 from one tenth to nearly three twentieths of an inch in length. 

 It is of a pale yellowish white color, with an internal dusky 

 streak, and is destitute of hairs. The head is round, and 

 partially retractile. The jaws are lateral and hooked; they 

 meet at the points, and are of a blackish color, and apparently 

 of a horny texture ; and they are distinctly to be seen even 

 with a pocket microscope. It is evident, therefore, that these 

 joint-worms are not the larvse of any Dipterous insect; they 

 are doubtless Hymenopterous larva?, and probably, from their 



