AuGus'f 1, 1803.] 



KNOWLEDGE. 



145 



fcimd, but the question was, how could the eggs, supposing 

 ' the insects to have originated from eggs, get into the centre 

 of a mass of vegetable tissue, when no pathway thither 

 could be discovered '? The difficulty was of course enhanced 

 by the prevalent belief that the galls were a natural product 

 of the plant, not diseased excrescences, and were, in fact, a 

 sort of h'uit of the plant, as much so as its ordinary and 

 legitimate fruit. 



Many explanations of the mystery were proposed. One 

 theory was that the eggs were derived from the ground, 

 and that they passed into the roots of the tree, and along 

 its vessels with the ascending sap, till ultimately they 

 reached their proper receptacle, which had been already 

 provided for them, and in which they were destined to 

 mature. Or, again, it was thought that there might be 

 germs floating in the air, which at last came in contact 

 with some part of the plant, to which they adhered, and 

 then the plant, pursuing its natural growth, grew round 

 the germs, and finally enclosed them. Another explana- 

 tion waa offered to the effect that, though the insects 

 themselves belonged to the animal kingdom, yet they were 

 a direct product of the vc(ictahle life which animated the 

 plant in which they were found ; that in fact they did not 

 arise from eggs or germs, but that whatever forces those 

 were that produced the growth of the ordinary parts of 

 the plant, leaves, flowers, fruit, or what not, the same 

 forces also led to the formation of the insects found in the 

 supposed secondary fruits. Indeed, it was gravely asserted 

 that one of the express purposes of the formation of fruits 

 at all was that they might beget and nourish these insects 

 found inside them. And yet, in this last supposition, 

 absurd as it may seem, we have — since the sole purpose of 

 the gall, so far as we can see at present, is to nourish and 

 shelter the contained insect^a sort of half-truth obscured 

 by the idea that the galls are a natural product of the tree, 

 of the nature of a fruit, but destined to produce and per- 

 petuate an animal ofl'spring instead of a vegetable one. 

 In the fact that the oak tree produced not only its ordinary 

 vegetable fruit, the acorn, but also an animal fruit as well, 

 the gall-insect, some saw a reason why the ancients 

 dedicated the tree to Jupiter. And then, lastly, there was 

 of course also the doctrine of spontaneous generation, 

 which could be lallen back upon when every other explana- 

 tion failed. 



The mystery thus attaching to the gall and its im- 

 prisoned inhabitant served not unnaturally to connect 

 them with occult science, and they were used for purposes 

 of prognostication. They were the repositories of Nature's 

 secrets, and it was according to the form their occupants 

 assumed that the character of the forthcoming season 

 would be determined ! The unpiei'ced galls were believed 

 to contain either a tly, a spider, or a worm. The lly was 

 of course the fully-matured gall-insect, and the worm was 

 its larva ; what the spider was it is not so easy to see, 

 unless galls containing mites or beetles were referred to. 

 However, if on opening the gall a fly was found within, it 

 was a presage of war ; if a worm, the price of the commo- 

 dities of life might be expected to rise ; but if the prisoner 

 turned out to be a spider, this was an ill omen indeed, 

 and the season would bring a dismal record of pestilence 

 and death. 



Of quite a diflerent character fi'om any of the galls we 

 have already considered are those x^retty adornments of 

 oak leaves called "spangles." They are flattish, circular 

 bodies, of a reddish or brownish colour, and attached in 

 considerable numbers to the underside of the leaves 

 (Fig. 6). They are fastened to the leaf at one point 

 only, by means of a m'inute stalk, so that they look 

 something like a tiny fungus, for which in fact they 



Fig. 6. — Portion of Oak Leaf with 

 Spangles ('Jfeui-oteriis lenliculnrlfj. 



were at one time mistaken. They are formed by various 

 species of a genua called Neuroterus, and the economy 

 of the insects is very 

 different from that of the 

 species we have already 

 considered. They are 

 long in coming to matu- 

 rity, and indeed scarcely 

 begin their development 

 as long as the galls re- 

 main attached to the tree. 

 The spangles appear in 

 the autumn, and after a 

 certain period of growth 

 become detached from 

 the leaves through the 

 severance of their short 

 little stalk, and fall to the 

 ground, leaving only a 

 small spot on the leaf to 

 show whence they have 

 come. They lie about at 

 the foot of the tree 

 through the winter, ab- 

 sorbing moisture from 

 the damp ground, and swelling considerably. Thus, 

 although severed from the tree that produced them, 

 and cut off from its supplies of sap, they are yet able 

 to remain succulent, and indeed to become still more 

 so than when on the leaves, and so can contribute to 

 the growth of their occupants. The grubs, therefore, 

 which are exceedingly minute till after the spangles 

 fall, feed chiefly during the winter, and the flies become 

 mature by about February or March in the following 

 year. Two of the best known of these spangle-galls 

 are those of Nvuroterm lenticnlaris and numi.<<matis. The 

 former are lens-shaped, hairy galls of a reddish colour, 

 and the latter are of a golden brown, like little silk buttons. 

 Both are gregarious, that is to say, large numbers of the 

 galls are foimd on the same leaf, sometimes so close together 

 as to interfere somewhat with one another's growth. 



An exceptional interest attaches to these oak spangles 

 and their occupants, inasmuch as they constitute one 

 of the best instances of the remarkable phenomenon of 

 heterogamy, or that particular variety of the alternation 

 of generations which consists of the regular succession of 

 two types of creatures, the one consisting of both males 

 and females and producing eggs in the ordinary manner, 

 the other consisting of females only and producing eggs 

 without impregnation, the whole series constituting in 

 reality but one species. We have spoken above of the 

 flies that issue from the currant galls and spangles by the 

 names by which they are generally known, and therefore 

 it will be seen that they are referred not merely to 

 diflerent species, but even to difl'erent genera ; it remains 

 now to point out that they are in reality not two distinct 

 insects, but only two stages in the history of one. It will 

 be remembered that the currant galls and spangles do not 

 appear at the same season, but that the former are very 

 short-lived, lasting for less than a month, while the spangles 

 appear later in the year, after the currant galls have passed 

 away, and last much longer. Thus one might naturally 

 wonder what becomes of the inhabitants of the currant 

 galls during the other eleven months of the year, and 

 what condition they are in, since they only take one 

 month to pass through their entire metamorphosis. It 

 now appears that during the rest of the year they exist in 

 another form, as inhabitants of the spangles. The 

 discovery of these remarkable facts was first announced by 



