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



with their present specific characters and specific habits, and if conse- 

 quently the Inquilines were never aboriginally Gall-makers, it seems 

 difficult to understand why there should not, for example, be inquili- 

 nous Tenthredo, Selandria, Dolerus, Emphytus, Gimbex, Lyda, Ce- 

 phus, Hylotoma , &c, &c, as well as inquilinous Nematus and inquili- 

 nous Euura. Or, in Mr. Wallace's caustic language, must we simply 

 "register the facts and wonder," (Trans. Linn. Soc. xxv, p. 31,) with- 

 out attempting to explain or account for them ? The advocates of the 

 Creative Theory, have, indeed, a very short and easy method of treat- 

 ment in such cases as these. — ' ; I am right and vou are wrono-. When- 



CD %/ O 



ever a fact turns up that is apparently inconsistent with my hypothe- 

 sis, I am not bound to explain it, because 1 am in the right. But when- 

 ever a fact turns up that is apparently inconsistent with your hypothe- 

 sis, you must explain it thoroughly and satisfactorily, under pain of 

 being nonsuited in the Court of* Science, because you are in the 

 wrong." 



V. As a general rule, Tenthredinidse are variable in their coloration, 

 many species most astonishingly so. I may quote as notable examples 

 Acordulecera dorsalis as described by Say, and Nematus s. pomum, n. 

 sp., as described by myself. On the other hand the allied family lch- 

 neumonidse, are generally very constant in their coloration. I have 

 been in the habit here for many years of breeding and preserving large 

 numbers of various species, and I am confident that this will hold good 

 as a general rule, though of course there are certain exceptions. Now, 

 assuming these facts to be as stated — and they are only a special ex- 

 ample of what I have called elsewhere the Law of Equable Variability 

 (Proc. &c. II, p. 213 and compare III, p. 424, note) — how can we 

 satisfactorily account for them, on the hypothesis of each Tenthredini- 

 dous and Ichneumonidous species having been separately created, and 

 not derived from some primordially pre-existing species ? 



VI. There are often very remarkable sexual differences in the color- 

 ation both of Tenthredinidse and of Ichneumonidse. As a general rule, 

 when such differences exist in Tenthredinidse, the % body is much 

 darker-colored than that of 9 . For example, when there are pale eye- 

 orbits in both sexes they are uniformly narrower in the % than in the 

 9 ; again, the % thorax or the % abdomen, or both, will often be black 



or mostly black, and the $ thorax or 9 abdomen, or both, red, yellow 

 or greenish, or mostly red, yellow or greenish. Contrariwise, the an- 

 teniue, when sexual differences exist in their coloration, are generally 

 paler in I than in 9 . being often, especially on the inferior surface. 



