Retrospective Criticism,- 4^6^ 



once clear up the doubt, since we are informed by them, (vol. iii. p. 214.) 

 that amongst the larvse (although chiefly of the lepidopterous tribes)' 

 which enclose themselves in silken cocoons, are " those brilliant beetles 

 frequenting aquatic plants constituting the genus Donacia F. ; and in a: 

 subsequent page (227.), when speaking of the situation, often very remote 

 from their place of feeding, in which larvae fabricate their cocoons, they 

 state, that that of Donacia fasciata is fastened by one side to the roots or- ■ 

 surculi of T'ypha latifolia." •> 



It does not appear to me improbable that E. S. was led to conclude- 

 that the cocoons in question were the fabrication of the perfect insect, in 

 consequence of his having found the perfect insect enclosed. He has, how-' 

 ever, omitted to state the precise time when he discovered them, which ' 

 would in some degree determine the question, although we may conclude' 

 that it was some time during the winter. A circumstance, however, which 

 I observed last October, induces me to consider that the insect attains its 

 perfect state in the beginning of the winter, and remains enclosed in its 

 cocoon until revived by the warmth of the following spring ; indeed, Kirby 

 and Spence confirm this supposition by observing (vol. iii. p. 293. n. c.) that 

 " insects of the beetle tribe, especially such as undergo their metamor- 

 phosis under ground, in the trunks of trees, &c., are often a considerable 

 time after quitting the puparium before their organs acquire the requisite ' 

 hardness to enable them to make their way to the surface." . i\ 



The following are the particulars of the circumstance above alluded tof 

 and several interesting enquiries arise upon it, which it is not my present 

 intention to enter upon. During the month of October, I have repeatedly 

 found upon the leaves of the oak a circular gall, when full grown about! • 

 the size of a boy's marble, on opening which I invariably discovered its in- v 

 terior to have been but very little eaten by the larva, the centre only being 

 occupied by a small circular cell about one sixth of an inch in diameter. 

 In some galls this cell contained a full-sized grub ready to transform to the 

 pupa, whilst in others that transformation had already taken place. In the 

 majority of instances, however, the cell contained a perfect gall fly, Cynips 

 quercus-folii * ; and Reaumur, who does not notice the circumstance above 

 mentioned of the discovery of the larva and pupa, has given the following 

 observations upon this insect : — " Quand la feuille tombe au commence- 

 ment de I'hiver, la galle tombe necessairement avec elle. J'en ai ramasse 

 de celles qui etoient tombees, et je les ai ouvertes dans le mois de Decembre ; 

 j'ai vu alors que le centre de chacune avoit une cavite bien spherique, qui 

 etoit le logement d'une mouche qui s'etoit tiree de sa depouille de nymphe, 

 mais qui attendoit que la rude saison fut passee pour sortir d'une cellule 

 bien close et en etat de la defendre par I'epaisseur de ses parois contre les 

 injures de rair."f — MemoireSy &c., vol. iii. mem. 12. p. 226. edit. 12mo, 

 and plate 39. f. 13 — 16. Rosel has also given most beautiful illustrations of' 

 this insect in all its stages, in his Der Monatlichy &c. vol. iii. pi. 52, 53. '• 



It only remains for me to notice the concluding interesting observation 

 of E. S. relative to the formation of the cocoon under water without the 

 water entering into it during the progress of its formation. Is E. S. certain 

 that the situation in which the cocoon was found was under water at the 



* Some of the flies appeared to me to be endeavouring to cut their way 

 out of the galls. 



f " In the month of December I opened some galls which had fallen with 

 the leaves at the commencement of winter, and in the centre of each I 

 found a spherical cavity tenanted by a fly, already escaped from its pupa- 

 rium, and only awaiting the departure of the cold season to emerge from 

 a cell well closed, and sufficient, from the thickness of its walls, to defend 

 the inhabitant from the- inclemency of the atmosphere." 



