THE JOINT-WORM. 559 



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 larvae. 

 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 micro- 

 scope. It is evident, therefore, that these joint-worms arc 

 not the larvae of any Dipterous insect ; they are doubtless 

 Hymenopterous larvae, and probably, from their abundance, 

 those of the foregoing Eurytoma. The other larvae, few 

 in number compared with the joint-worms, are distinguished 

 therefrom by their inferior size, and whiter color, and by 

 being sparingly covered with short hairs. Their heads are 

 round, are provided with blackish hooked jaws, and have 

 two little tubercles on the front. I judge them to be the 

 young of one of the parasites, probably of the Torymus, 

 described on a former page. 



The foregoing account might be thought to afford con- 

 elusive evidence that the Eurytoma alone was the author 

 of the mischief done to the wheat and barley, and that it 

 is not a parasitical insect. In favor of this conclusion, we 

 have the fact that hitherto no person has succeeded in 

 obtaining from the diseased wheat-straw so much as a 

 single specimen of Cecidomyla ; while both the wheat and 

 the barley straw have yielded to several observers, in 

 repeated instances, numerous specimens of the same kind 

 of Eurytoma, and nothing else, saving an extremely small 

 number of lesser parasites. The determination of this dif- 

 ficult and interesting question is of much importance in a 

 scientific and an economical point of view. The groat 



