558 H Y.MKNOPTERA. 



to me tlie result of liis interesting observations. lie lias 

 come to the conclusion that the joint-worm is the larva of a 

 Hymenopterous, and not of a Dipterous insect. lie finds 

 that the parts of its mouth are veiy different from those 

 of the dormant larva of the Hessian lly (the latter ex- 

 tracted from its flax-seed case before it had undergone any 

 change of form), and that the mouth of the former agrees 

 essentially with that of the larvae obtained from galls of 

 the oak. In the mouth of the joint-worm he observed that 

 " the mandibular hooks cross each other on the middle line," 

 while in the Hessian fly larva the " two hooks are directed 

 downwards." His samples of diseased wheat-straw of the 

 prcA'ious year yielded him, in the spring, numerous speci- 

 mens of the Eurytoma, 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 Em'ijtoyna^ 

 and probably parasites. In several 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 sum- 

 mer, 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 larvae, and also some of the parasitical 

 worms, found in the straw, and has made for me several 

 macrnified sketches of them. Both kinds are found to differ 



