1864.] 01 5 



has been described by Dr. Fitch ; and it is likewise altogether too small 

 for the Lepidopterous pupa, whose exuviae I detected in this situation 

 T incline to believe that these are the holes through which some Grall- 

 gnat a trifle smaller than 0. s. bafafas has made its exit. At all events, 

 there is no insect known to inhabit the Black-knot, except the very 

 rare S. curcuUonis, to which they can possibly be referred. On cut- 

 ting into these specimens, their internal structure is found to be the 

 same as that of S. batatas^ viz. fibres radiating from the axis of the 

 twig, but the intervening matter is more woody than spongy. There 

 have been so many inquilines boring them in all directions, as may be 

 seen from the quantities of "frass" they have left behind them, that 

 it is difficult to ascertain the structure of the cells. In a few speci- 

 mens, however, which were mostly in their natural condition, I recoff- 

 nized cells, which appeared to nie, on comparing the two together, to 

 resemble very strongly those of Cec. s. hufnfas. and to be arranged 

 almost exactly in the same manner; and in these cells there was no 

 '■ frass" as there always is in the irregular holes inhabited by Curcu- 

 lionidous. Tenthredinidous or Lepidopterous larvae, o/v/. Dr. Fitch 

 gives as a reason why the Black-knot cannot be a gall, that •' always 

 in galls one or more hard, seed-like bodies are found in the centre, in 

 which the young of the fly producing them is inclosed." (Rrp. Cure. 

 (iiuJ Bl. Kt. p. 22.) This is not true of any Cecidomyidous gall known 

 to me, though it applies very well to Cynipidous galls. Hence this 

 argument only proves that the Black-knot is not made by a Gall-fly, 

 but is of no force whatever against the hypothesis of its being made by 

 a Gall-gnat. \th. Specimens are said by Dr. Fitch to occur sometimes 

 •' wholly free from the Curculio larvaj and all other worms." {Ibid p. 

 22.) Just so in the Cecidomyidous Willow-galls .S'. verruca, S. semen 

 and S. senlfjma, very many galls, be the cause what it may, are solid 

 and tenantless; and out of nine specimens of the Cecidomyidous gall 

 ^S*. noduluii, I found two untenanted by any larva and unbored. (See 

 above p. (300.) bth. I know by experience how difiicult it is to rear 

 Cecidomyia to the imago from galls severed from the parent tree, un- 

 less fresh specimens are gathered every few weeks to replace the old 

 ones in the breeding-jar. (See above p. 574.) It does not appear that 

 Dr. Fitch took this precaution, and hence, assuming the Black-knot to 

 be the work of a Gall-gnat, I am not at all surprised at his failing to 



