181 



opening in the top of the gall, where it is retained while the fly- 

 disengages itself from the pupa-skin. The peculiarity of this 

 kind of transformation consists in the fact, that the conversion to 

 the pupa is effected without any moulting of the larva-skin, which 

 is retained in a modified form, and becomes the proper skin of 

 the pupa. 



The American wheat-fly appears to be identical with the Eu- 

 ropean Cecidomyia tritici. When the orange-colored larva of this 

 species is fully grown, its body contracts and becomes loosened 

 from the outer skin, which is so thin and delicate that the included 

 larva may be seen through it. In this condition the larva remains 

 quiescent several days, after which it extricates itself from its 

 filmy skin, and recovers its activity, but takes no more food. The 

 wheat-ears are often found full of these delicate cast skins, which 

 are so light as to be wafted away by every breeze. Sometimes, 

 though rarely, this moulting does not occur till after the larvae 

 have left the grain. Their descent is generally made in the 

 night, and is facilitated by the heavy dews or falling rain. Hav- 

 ing moulted and descended to the ground, the larva buries itself 

 just below the surface, and there remains in a dormant state, and 

 without change, till the following spring. A few days, at most, 

 before its final transformation, this larva becomes a pupa. The 

 manner in which this transition is effected is altogether similar to 

 that w^hich has been observed in O. salicis. The abdominal por- 

 tion of the larva-skin undergoes little or no change ; the forepart 

 of the body becomes red, swollen, shining, and apparently gela- 

 tinous, and allows the budding limbs and wings to push outward, 

 so that each member becomes enveloped in its own process of the 

 yielding cuticle. The pupa then, though covered still with the 

 larva-skin, wdiich is merely modified by extension or growth, or 

 both, to suit the changed condition of the insect, is not a true 

 coarctate pupa ; it is a naked pupa, with its limbs and wings ex- 

 posed and free, and folded upon the breast. The insect continues 

 in the pupa state only a very few days ; it then makes its way 

 to the surface of the ground, casts off its modified larva or pupa 

 skin, and appears in the winged form. This is the only Dipterous 

 insect which is know^n to cast off and abandon its skin while in 

 the larva state. Other species of Cecidomyia, however, may be 

 found to exhibit the same peculiarity. 



