Callirhytis seminator
The three "Willow galls produced by Sawflies, that we have already treated of in this Article, are all " monothalamous." The two Oak-galls that we are now about to describe are both of them " polythalamous " or many-celled; that is, each gall contains an indefinite number of distinct cells, each of which is inhabited by a single gall-making larva. In the "Wool-sower gall (Fig. 45 a, sectional view), these cells may be seen in the middle of the gall, and are little pip-like bodies having much the appearance of a canary-seed, one of which we represent enlarged at b, so as to show the hole through which the perfect fly has made its exit. The reader can form a tolerably good idea of the shape and make of this fly, by referring to the drawing given in our first "Volume (page 104, fig. 81) of an allied gall-fly, which however is thrice as large and which differs further from the Wool-sower Gall-fly by the wings being much marked with brown-black.
The Wool-sower gall is met with exclusively on the "White Oak, and like the Oak-fig Gall to which we formerly referred (Vol. I. p. 101) is, not a bud-gall, but a true twig-gall, growing early in the spring out of the bark of the twig itself. Mr. Bassett (Proc. Ent. Soc. Phil., 11, p. 331) broaches the theory that the Wool-sower gall and Osten Sacken's Q. operator gall are not twig-galls, but true bud-galls, and that "their cells are modified leaves, the silky fibres covering them being only a monstrous development of the pubescence always observable on young leaves." But 1st: As to the Oak-fig gall, we have already recorded the fact that "this mass of subglobular galls about the size of peas is clustered densely around the infested twig, without in any wise interfering with the normal development of the buds." {Ibid. VI. p. 275.) We may remark by the way that we have recently found the Oak-fig gall upon un- doubted Bur Oak {Q. macrocarpa), although it had been previously supposed that it never occurred except on White Oak (Q. alba). 2d: As to the Q. operator gall, we ascertained long ago that it is a deformation, not of the twig, nor of the leaf-buds, but of the male flower of the species of Oak, upon which alone we have hitherto met with it, namely the Black Oak (Q. tinctoria); for the Black-jack Oak (Q. nigra), upon which Osten Sacken first discovered it, does not grow in North Illinois. Even on this last oak Osten Sacken records the fact that his gall occurred exclusively ''on young flowering branches. (Ibid. I. p. 266). 3d: As to our "Wool-sower gall, if the cells were a deformation of the buds, we should surely find them gathered into two distinct groups around the bud on each side of the oak- twig that gave origin to them, as in the gall which is next to be noticed; whereas they are always evenly distributed around the axis of the twig. Besides the pip-like cells to which we have already referred, it is composed of little else but a mass of whitish, spongy wooly matter, the external surface of which is of a pretty rose-color early in the season, but towards the middle of the summer assumes a rusty brown shade. At every period of the year the outside of the gall is invariably studded with numerous conical projections or teeth, which are very characteristic, though our engraving scarcely shows them as pointed as they arc in nature, and Dr. Fitch's figure omits them entirely. The perfect Gall-fly comes forth about the end of July, and the female must then, after coupling with the males, puncture such White-oak twigs as she judges to be suitable for her purpose in a very great number of adjoining points, dropping an egg along with a minute drop of poison into each puncture. Until the following spring these eggs always lie dormant, as in many other such cases; for Dr. Fitch is altogether wrong in asserting that there are two distinct broods of Wool-sower Gall-flies every year, generating two distinct sets of galls.* We have examined hundreds of these galls at all seasons of the year; and never yet did we find one at a later period than the end of July, that was not bored up, empty and untenanted. In fact, it is not often that they remain on the twigs through the winter; for when ripe they are attached so very slightly to the twig upon which they grow, that they can readily be slipped up and down like the beads of a rosary, and the least lateral jerk displaces them entirely.
