214 [December 



the wing, which almost always in the bulla} A . . . E, but scarcely ever 

 in the spots i^and G, adjoins the white spot on the vein itself.* 



To entomologists who have worked much on any particular group or 

 groups of insects, the facts stated above will, I suspect, seem not at all 

 extraordinary. For many similar cases of Coloration al Unity occur in 

 every Order; and it has repeatedly happened to myself, and I doubt not 

 to others, that, after having examined numerous species belonging to a 

 given genus, I come at last upon one with a particular spot or a particular 

 stripe conspicuously developed in a particular locus, and, on recurring 

 to the species already examined, find more or less faint traces of the 

 same spot or the same stripe in every one of them. But to the student 

 in other departments of Natural History, where the number of species 

 is so very much smaller than in Insects, and where consequently there 

 is no such opportunity to form very extensive generalizations, the phe- 

 nomena detailed above will appear, perhaps astonishing, perhaps incre- 

 dible, perhaps false. They are nevertheless strictly true; and anyone 

 may easily satisfy himself of their truth, by selecting at random any 

 species of Ichneumon and holding up its wings to the light under a mo- 

 derately good lens. 



The question naturally occurs here to the philosophic mind — What 

 is the MEANING of all these facts ? Why do the same bullje in the 

 same loci occur in so many distinct species of the same genus? Why 

 do not some species have these bullae located on some of their other 

 veins, or on some other part of the same vein ? Why, for example, is 

 there never a bulla on the basal side of the angle of the first recurrent 

 vein, either in Ichneumon or in any other Ichneumonidous genus? 

 Why are there not sometimes six or eight or ten bullae ? Why are 

 there not sometimes none at all ? In every species of Ichneumon we 

 find, it is true, without exception, a pentagonal or subpentagonal 

 areolet and a very short ovipositor. But the reason of this is obvious. 

 If the insect was without these characters, it would not be placed in 

 the genus Ichneumon ^hecauae these are some of the established generic 

 characters of Ichneumon. Yet so far is it from being the case, that the 

 bulhc are an established generic character of Ichneumon, that they do 

 not appear to have been even noticed hitherto, except incidentally in 

 the descriptions of a few species. Look at the figure given above. 

 Anyone can see that the seven white spots on it might be arranged on 

 the wing in millions and millions of diiferent patterns. Why then in 



*I observe that in Thyreodon and Ophion the spots i^and G often extend on 

 to the membrane of the wing, i)recisely as in bullre A . . . . £. 



