of certain species of Willow. — Part 2nd. 287 



III, p. COS,) as apparently Cecidomyidous. Ampelopsis boars 1 gall, evi- 

 dently from its structure Cecidomyidous. Acer bears 1 Cecidomyidous 

 gall described by Osten Sackeu and 1 n. sp., besides 2 Acaridous galls 

 n. sp. And lastly Negundo bears 1 Acaridous gall n. sp. The sum 

 total of Cecidomyidous galls is 56 in the first list on eight genera of 

 plants and 10 in the second list on nine genera of plants, including 

 two galls of doubtful origin j total 72 galls, occurring on seventeen differ- 

 ent genera of woody plants. The sum total of Acaridous galls, exclud- 

 ing some mere deformations, is 7 in the first list on four genera of 

 plants, inclusive of one gall of doubtful origin, and 13 in the second 

 list occurring on ten genera of plants; total 20 galls, occurring on four- 

 teen different genera of woody plants. Grand total 92 galls, occurring 

 on twenty-five different genera of woody plants, six out of the twenty- 

 five bearing both kinds of galls. 



Now look at these statistics, to see if they will teach us anything. 

 On the one hand we have 14 genera of woody plants producing fully 

 96 galls other than Acaridous and Cecidomyidous galls ; and on the 

 other hand we have no less than 33 genera of the same group of plants, 

 which on the most diligent search I have not found to produce any 

 such galls ; and which, so far as I am aware, have not been recorded 

 by North xVmerican authors as producing them. Why should this be 

 so ? Why should 96 galls be distributed so unequally among 47 ge- 

 nera of the same group of plants, that 33 out of the 47, or more than two- 

 thirds of the whole number, have none at all, and a single genus, Quer- 

 cus, monopolizes more than one-half of the whole number ? We can- 

 not say that all these 33 genera are naturally incapable of producing 

 galls; for at least 15 of the 33, and probably more, produce either Ac- 

 aridous or Cecidomyidous galls or both. Why, then, do they not pro- 

 duce other galls as well ? Why, as a general rule, is each gall-making 

 genus of true insects, with the exception of Cecidomyia and its subge- 

 nera, restricted to a single geuus of plants ? Why do so many species 

 of the same genus often occur on the same genus of plants — 58 N. A. 

 species of Cynips, for example, on the single genus Quercus, besides 

 many undescribed N. A. species, and besides the 100 species of Cynips 

 tbat infest the genus Quercus in Europe ? On the Creative Theory, 

 all this is an inexplicable mystery. On the Derivative Theory, we see 

 at once why it should be so.' For if our modern species were genetic- 

 ally derived from pre-existing species, several new species being gene- 

 rated from one old one, and wbole groups from time to time becoming 

 extinct, the actual state of facts, as it has been presented above, is pre- 



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