Who, once more, that reflects that if any of the superior animals are deprived of a limb it can never be reproduced, and that in insects the same circumstance occurs; while spiders and Crustacea if they lose a leg have the power of reproducing it, and the Mollusca if they are decapitated can gain a new head,—will consent to their being placed after any of these animals[1155]?
Lastly, who that recollects that the Mollusca are hermaphrodites, like most plants, bearing both male and female organs in the same body,—but will allow that insects, in which the sexes are separate as in the Vertebrates, must be more perfect, and of a higher grade[1156]?
ii. We now come to the Classes into which the Annulosa are divided. This term appears first to have been employed by Tournefort, and was adopted by Linné[1157]. As the nervous system of animals furnishes the most prominent distinction of a subkingdom, so the circulation of their fluids, and their respiration necessarily connected with it, seems best to point out the classes into which it may next be resolved. But having fully explained my ideas on this subject in a former letter, I need not here repeat what I then said[1158].
iii. As we have subkingdoms, so we may also have subclasses, or such large divisions of a class—not founded upon internal organization or any of the primary vital functions, but upon different modes of taking their food, or such other secondary characters—as include more than one Order. To this description Clairville's Mandibulata and Haustellata appear to me to belong, which I think are by no means entitled to the rank of Classes; for whoever compares these two tribes together will at the first glance be convinced, by the numerous characters they possess in common, notwithstanding the different mode in which they take their food, that they form one connected primary group. This circumstance, therefore, only furnishes a clue for their further subdivision into two secondary groups, separated by distinctions certainly of a lower value than those which separate the Crustacea and Arachnida from Insecta. This is further confirmed by the variations that take place in their mode of feeding in their different states; some from masticators becoming suctorious (Lepidoptera), and others from being suctorious becoming masticators (Myrmeleon, Dytiscus, &c.),—which shows that this character does not enter the essential idea of the animal.
iv. Next to Classes and Subclasses we are to consider those groups of insects that are denominated Orders. The characters of these at first were taken principally from the instruments of flight or the absence of them; and the name appropriated to each Order by Linné, after Aristotle, had reference to this circumstance. But this alone does not afford characters sufficiently discriminating: for though to an accurate observer a difference in these organs appears to be characteristic of most of the Orders, yet in some it is not easily detected or defined. In the Neuroptera there are as many different types of wings as there are of tribes or suborders. So that it seems not possible so to construct the definition of every Order, as to take its character from the organs of flight alone. Linné was sensible of this, and was compelled to have recourse to subsidiary characters in the majority of his: his observation therefore with regard to Genera,—that the character does not give the genus, but the genus the character[1159],—applies equally to Orders; and the characters included in the definition of an Order, should be the result of a careful examination of its component groups.
On a former occasion I named to you the Orders into which it appeared to me the Class Insecta might be divided[1160]; they were these. Coleoptera; Strepsiptera; Dermaptera; Orthoptera; Hemiptera; Trichoptera; Lepidoptera; Neuroptera; Hymenoptera; Diptera: Aphaniptera; Aptera. I then briefly explained them merely for the sake of illustration, and that you might know what description of insects were meant when these Orders were mentioned in my letters, without intending to affirm that I had arranged them in a natural series, or that all of them were perfectly natural. I shall now consider them separately, and conclude with giving my sentiments as to which should be placed first.
* orders in which the ordinary Trophi all occur, or the Mouth is perfect[1161]. (Mandibulata.)
1. Coleoptera[1162] (Eleutherata F.). Aristotle may be called the founder of this Order, since he both named and defined it[1163]. Both his name and definition were adopted by Linné; and the former (with the exception of Fabricius and his school) by all succeeding Entomologists. To his definition Wings in a sheath[1164], other characters have been added; as the folding of the wings, and the straight suture by which the elytra are united[1165]. Aristotle's character, though to be found in the great majority of the Order, is not universal, since there are some beetles that have neither wings nor sheath, as the female glow-worm; and many that though they have the sheath have no wings, as Meloe, many Carabi, &c. To the transverse folding of the wings there are also exceptions; as in Buprestis, Molorchus, &c. The straight suture by which one elytrum exactly coincides with the other without lapping over, fails in Meloe: so that no one of these characters can be called universal in the Order; but as an exception or two does not invalidate a rule, and these are sufficiently universal for the purpose of pointing it out, they may be retained. Perhaps it will be an improvement to add the kind of the metamorphosis, which, as far as known, prevails universally.
Def. Metamorphosis incomplete[1166].