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 he 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 
Ilymenopterous 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- 
clusive 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 Cecidomyia ; 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 great 
