Mr. MacLeay found that in his quinary groups one of each five contained genera or species related to other genera or species in each of the other four groups. That I may be thoroughly understood, I will quote the author's own words:--"In almost every group which has been set before the reader, he must have perceived that one of the five minor groups into which it is resolvable, bears a resemblance to all the rest; or, more strictly speaking, contains types which represent each of the four other groups, together with a type peculiar to itself."[26] As far as my observation has extended, this is universally the case; and whether the total number of groups be five or seven, I think I am safe in asserting that the only possible way of making these types, thus representing groups, approach such groups, is to place the heterogeneous group in the centre, and the homogeneous groups around it; taking care that the type peculiar to itself be its very centre, its "heart's core." Such a heterogeneous group, then, is Neuroptera: its characters as given,[27] I believe, perfectly correct; and can any one say they are sufficient? Certainly not; but had I described it thus--Class VII. Neuroptera, central, partaking of the characters of all the others, I think a better character could not have been given. This class contains a type peculiar to itself--the genus Libellula of Linnæus: a genus so distinct, that several authors have supposed it to constitute one of the primary divisions of Insecta. It is, however, merely the Neuropterous type, the very essence of the class; and many of its species, Anax Imperator for instance, proclaim themselves by their imperial flight, their enormous size, their richly variegated colours, their despotic and cruel habits, emperors of the insect world. In this group we find the organs of sight, manducation, and locomotion, carried to a greater degree of perfection than we ever meet with, except in similar centres: like the king of birds, the dragonfly is unrivalled among his kind. From Libellula, the centre, we descend at once to Tinodes, or Psyche, on the circumference of the circle. Supposing Psyche to be the approaching genus to Lepidoptera, I think I need not enter very diffusely on the similarities. Passing to the right, we find that Diptera will next touch the central class; in which, after leaving the Phryganeæ, we have now arrived among the next group, or sub-class, Ephemeræ: and here, as we might expect, the inferior wings become much diminished--at the point of contact obsolete.[28] The flight, instead of being solitary, is in company, gracefully and gently rising and falling. The parts of manducation are become obsolete; while, in habit and appearance, the insect imitates the Tipulæ and Chironomi, so exactly that the naturalist is foiled in his endeavours to distinguish between them, as they joyously dance together by myriads in the rays of the setting sun. [26] Horæ Entomologicæ, p. 518.