288 Benj. D. Walsh on the Insects inhabiting the Galls 



cisely that which we should, reasoning a priori, expect to meet with. 

 Surely, therefore, upon general principles, a hypothesis, which accounts 

 clearly and satisfactorily for a great mass of phenomena, is more likely 

 to be a correct one, than a hypothesis which accounts for nothing, and. 

 while it mercifully spares our Seasoning powers, draws most largely 

 and exorbitantly upon our Faith. 



And now, in conclusion, it is but fair dealing towards the American 

 reader, as in the former part of this Paper I expressed considerable 

 skepticism in regard to Wagner's supposed discovery of viviparous lar- 

 vae, (pp. 571 — 4 and 641 — 4,) to take this opportunity of stating, that 

 I am informed by Baron Osten Sacken that Wagner's facts have been 

 verified by the German entomologist Gerstaecker and that they are 

 generally believed in Germany ; and that Mr. Darwin writes me word 

 that they are believed by the distinguished English naturalist, Sir J. 

 Lubbock. It further appears, from what Baron Osten Sacken tells 

 me, that the prolific Cecidomyidous larvae, instead of belonging to the 

 genus Cecidomt/ia, as I had been originally led to suppose, (Proc. &c. 

 Ill, pp. 571 — 2,) are now ascertained to belong in reality to a rather 

 anomalous genus, which has been named Miastor, and which "has been 

 found to be almost identical with Heteropcza Winnertz." Respecting 

 this last genus Loew observes, that "it seems to harmonize in many 

 points with the genera of the first section, [which includes Cecidomyia,~\ 

 but differs very strikingly by the totally different structure of its tarsi." 

 (Dipt. iV". A. p. 7.) Hence the principal stumbling-block which lay 

 in my path — namely, that different species, belonging to one and the 

 same genus Cecidomyia, should have such essentially different and he- 

 terogeneous habits — is removed at once; and I beg leave hereby to 

 recant and disavow my former skepticism as to Wagner's very re- 

 markable and important discovery. 

 Rock Island, III., August 31, 1866. 



ERRATA. 



Page 237, line 4 from bottom, for "Pristophora" read "Pristiphora. 

 Page 268, lines 24 — 5, for "scutlelatus" read "scutellatus." 



