(U6 [December 



rear Grall-gnats from it. Qth. I have not seen a line anywhere in Dr. 

 Fitch's writings, from which it could be inferred, that he was aware of 

 the peculiar character which distinguishes the larva of the Grall-gnats 

 from all other larvae, viz. the breast-bone. He has described in his 

 Reports the larvae of three different G-all-gnats. Cec. grossnian'ae Fitch, 

 C. 2)seu(?ac((ciee Fitch and C. rohiiiise Hald., yet in no one of these 

 three cases does he breathe a syllable on this very important topic ; and. 

 as we have already seen, in the description of the larva of his Ore. 

 salkis he mistakes the breast-bone for a part of the head. (See above 

 p. 597.) Hence, even if he had found minute Cecidomyidous larvae 

 in the Black-knot, he might very possibly have mistaken them for the 

 similarly apod larvje of the Curculio. which he says that he found in 

 '' ALMOST ALL OF THEM." Just SO the botauist Schweiuitz. who asserts 

 that the \ai'\-x of a minute C//nips are found in the Black-knot, (quoted 

 Harris InJ. Lis. p. 80,) seems to have mistaken Cecidomyidous larvae 

 for Cynipidous larvae j and as we have already seen, (p. 551.) Euro- 

 pean authors formerly made the same confusion in the case of the in- 

 sect of the " Rose-willow." 7fh. Grall-gnats, as shown above (p. 552), 

 occur on an immense number of different and widely distinct genera of 

 plants, and the other gall-making genera of insects on comparatively 

 very few genera of plants. Consequently, if the Black-knot is a true 

 gall, and not a mere disease, we may infer a jjriori that it is far more 

 likely to be the work of a Gall-gnat than of any other of the gall in- 

 sects. Sth. Just as, with all the Willow-galls originated by (rail-gnats 

 or Saw-flies upon twigs or limbs, and also with similar Oak-galls origi- 

 nated by Grall-flies, and with a hitherto undescribed, oval, Lepidopte- 

 rous Gall on the twigs of the shrub called Amorpha fruticosa, which 

 I have long noticed and which is produced by Wnlsliia amorphcUa 

 Clemens, and finally with the terminal gall of Bf/rsocrypfa vagahumla 

 Walsh, on the tips of the twigs of several poplars, (see Proc. Eat. Soc. 

 Phil. II. p. 462.) the twig — unless it is pretty large or unless as in S. 

 nodulus n. sp. the insect is very small and only one of them — is always 

 killed by the presence of the gall ; so with the Black-knot, as I have 

 myself observed, the smaller limbs are killed by it and the larger ones 

 — say of J or i inch in diameter — are not so killed. On the other hand 

 the pseudo-gall of the Coleopterous Siperdu inortiata Say, which grows 

 on one of these same Willows, though the actual damage it does to the 



