8 Insects Injurious to Vegetation. [Jan., 



dominal segments are distinctly marked by strongly impressed 

 transverse lines, and are of a milk-white color, the thorax and 

 head being of a delicate pale pink-red, and the feet translucent- 

 white. On the anterior margin is a chestnut-brown crescentiform 

 mark. It will hence be perceived, that in all the details of its 

 form, the pupa of the Hessian fly coincides precisely with those 

 of the other species of this genus which have been described. 



Its change into a fly. — The time for its final transformation 

 having arrived, the pupa breaks open and crawls from its pupa- 

 rium or flax seed case, and works its way upwards within the 

 sheath of the leaf, until it arrives at some cleft in the now dead, 

 brittle and elastic straw; through this cleft it gradually, by bend- 

 ing from side to side, crowds its body until all except the tip 

 of the abdomen is protruded into the air, the elasticity of the 

 straw causing it to close together upon the tip of the abdomen, so 

 much as to hold the pupa in this situation, secure from falling to 

 the ground; and as if to preserve the body in a horizontal posi- 

 tion, the feet are slightly separated from the abdomen, and di- 

 rected obliquely downwards, with their tips pressed against the 

 side of the straw, thus curiously serving, like the brace to the 

 arms of a sign post, to support the body from inclining down- 

 wards. Thus securely fixed, and now freely exposed to the dry- 

 ing influence of the atmosphere, the outer membrane of the pupa 

 speedily exhales its moisture, and as it becomes dried, cracks apart 

 upon the back part of the thorax; out of this cleft the inclosed 

 fly protrudes its head and thorax more and more, as it gradually 

 withdraws its several members, the antennae, wings and legs, from 

 the cases in which they are respectively enveloped — a process 

 analagous to that of withdrawing the hand and its several fingers 

 from a tight glove; until at length entirely freed, the now lull- 

 fledged and perfectly formed fly leaves its pupa skin and mounts 

 into the air. 



Peculiarity in its mdamorphoses. — It is sufficiently apparent 

 from the account that has now been given, that the Hessian fly 

 differs notably from all its congeners in one important point in its 

 transformations. From all the observations that have been hither- 

 to made, the cecidomyians correspond with the other tipulides in 

 this prominent particulai' — that their pupa? are naked. Other 

 species, at least many of them, after completing their growth, 

 cleave from their skins in the same manner that the Hessian fly 

 does, but when the separation is formed, the inclosed worm inva- 

 riably crawls from and forsakes its larva case. It is thus, even, 

 contrary to what has been hitherto supposed, with the C. tritici. 

 Since my essay upon that species was published, I have clearly 

 ascertained that the mature or dormant larva does cast its skin. 

 So far as I am aware, moreover, the cast skins in the several spe- 



