fietrospective Criticism. 455 
once clear up the doubt, since we are informed by them, (vol. iii. p. 214.) 
that amongst the larve (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 Z'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. ii. 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.” 
The following are the particulars of the circumstance above alluded to ; 
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 If invariably discovered its in- 
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 Vhiver, la galle tombe nécessairement avec elle. J’en ai ramassé 
de celles qui étoient tombées, et je les ai ouvertes dans le mois de Décembre ; 
jai vu alors que le centre de chacune avoit une cavité bien sphérique, qut 
étoit le logement dune mouche qui s’étoit tirée de sa dépouille de nymphe, 
mais qui attendoit que la rude saison ftit passée pour sortir dune cellule 
bien close et en état de la defendre par l’épaisseur de ses parois contre les 
injures de Vair.” + — Mémoires, &c., vol. ii. mém. 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 Monatlich, &c. vol. iii. pl. 52, 53. 
It only remains for me to notice the concluding interesting observation 
of E. 8. relative to the formation of the cocoon under water without the 
water entering into it during the progress of its formation. Is E. 8. 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. 
+ “ 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.” 
