1865.] * 209 



the similarly different colorational forms of two such closely allied ge- 

 nera as Dori/phora and Chri/wmela have, ages and ages ago, all pro- 

 ceeded from a common origin ? 



Genus Ichneumon. (Hymenoptera.) 

 There is another and a still stronger case of what I have called the 

 *' Unity of Coloration," which, as it is a very curious one, and does not 

 appear to have been hitherto noticed or elucidated by any author, I 

 may be excused for dilating on. In fact, colorational characters such 

 as these, which prevail throughout several species or throughout whole 

 genera, are usually neglected by those entomologists who occupy them- 

 selves in establishing new genera, because the commonly received opi- 

 nion is that genera must be founded, not upon colorational, but upon 

 structural characters; and by those who occupy themselves in describ- 

 ing new species, because, being found indifferently in many species, 

 they are of little or no value as specific distinctions. Yet the very cir- 

 cumstances, that cause them to be neglected by these two classes of 

 writers, are precisely those which render them of pre-eminent interest 

 to the philosophic naturalist. 



The annexed figure represents — magnified about three diameters — 

 the front wing of any species of Ichneumon with blackish or fuliginous 



-4^__ /H wings, e. g. viola Cresson, Jiavicor- 

 nis Cress., scnichts Cress., cincticor- 

 nis Cress., scdestus Cvess., mnlacus 

 Say, morulus Say, devinctor Say, 

 > j^~"°' centi-afor Say, grandis Brulle, or 



riifiventris Brulle. It will be observed that there are five white spots 

 on it, .1 . . . E, which extend beyond the limits of the vein on which 

 they are situated into a blister-like expanse, that has much the appear- 

 ance of a spot of white mould. Besides these five, there are two mi- 

 nute spots. F and G, which scarcely ever extend beyond the limits of 

 the vein on which they are located. The hem of all these spots is per- 

 fectly definite and never differs in any species. A is small and often 

 subobsolete, and is invariably located on the internal side of the areolet, 

 and so well forwards as to touch the radial area. B is large and obvi- 

 ous, and is invariably located on the external side of the areolet, and 

 almost always slightly behind the middle of the cross-vein which it be- 

 strides. C is large and obvious, and is invariably located about mid- 

 way between the areolet and the obtuse, salient angle of the second 

 recurrent nervure. which angle, as in the figure, often has a short stump 

 of a vein proceeding from it. D is small and sometimes subobsolete. 



