6 Inffeds Injimovs to Vegetation. [Jan., 



mere empty fold of the membrane, without any inflation sufficient 

 to make room for internal viscera. At this end is often observa- 

 ble one or two little brush-like granules, resembling those on the 

 soles of the feet of some carabidous insects. (One of these is in- 

 dicated on the anterior edge of fig. i.) Are these the relicts of 

 the suctorial mouth of the larva? This larva case is compara- 

 tively tough and leather-like at first, but becomes more brittle and 

 also darker with age. 



Character of the dormant larva. On carefully opening the 

 larva case just described, a worm (fig. k.) is found within it, 

 scarcely different in any respect from what it was immediately 

 before entering upon this flax seed state. It has the same oval 

 form, opake milk-white color, and green, cloud-like visceral spot 

 or line beneath. The nine segments into which it appears divid- 

 ed, however, are now much more distinctly marked than they pre- 

 viously were, the transverse lines being more deeply impressed, 

 and the margins showing corresponding crenatures. No traces of 

 the members of the future fly are yet discernible. The insect now 

 undergoes no further change, for a period of five months or more. 

 Enveloped in its flax seed like mantle, and reposing at the root 

 of the now lifeless grain, it is buried beneath the snows of w'inter. 

 Over one half of its entire term of life is therefore passed in this 

 state. 



Error in previous accounts. This is the stage of this insect, 

 which has been spoken of by all preceding writers as its pupa or 

 chrysalis state. Upon a close observation of the Cecidomyia trit- 

 ici, the writer succeeded in discovering that that species had, w^hat 

 some had conjectured, but none had actually observed, a regular 

 pupa form, identical with that of other species of Cecidornyia, 

 whose metamorphoses had been fully described. It hence appear- 

 ed necessary to distinctly mark that long period of inactivity 

 which intervenes in the wheat fly, after the larva has completed 

 its growth, and before it enters its pupa state; it was therefore, 

 during this state of its life denominated a dormant larva, in my 

 essay upon that species. It occurred to me wdiilst writing out 

 that essay, that the dormant larva state of the wheat fly, was ex- 

 actly analagous to the flax seed state of the Hessian fly, and in a 

 note, my suspicions were expresetl that the real pupa of the Hes- 

 sian fly had never been detected. The ample oj)portunities which 

 I have since enjoyed for investigating this species, have enabled 

 me fully to trace out this point in its transformations, and to show 

 that it is not till near tiie close of its flax-seed period of existence 

 that the Hessian fly puts on its pupa form. In penning the note 

 just alluded to, I had overlooked a passage in Mr. Herrick's last 

 paper, from which it is obvious that he has seen the real pupa of 

 the Hessian fly, although he still speaks of its pupa state as com- 



