I have before expressed my sentiments upon several of these Orders[1443]: I shall not here repeat them, but shall merely observe, with respect to those I have not adopted, that, though perhaps not entitled to rank as Orders, most of them form natural groups. His Orders, however, of Arachnida must be excepted from this remark, since they are evidently artificial. His analyses of his Orders, though in general they give natural groups, are usually not carried so far as those of M. Latreille, so as seldom to indicate what may properly be denominated families. He has made his nomenclature for his so-called families more uniform and satisfactory than that of the French Entomologist: and we may say, with respect to the extent and effect of his zoological labours,—Nihil non tetigit, et omnia quæ tetigit ornavit.
7. Era of MacLeay, or of the Quinary System. I have more than once stated to you in my former letters the bases upon which the system which I am in the last place to explain to you is built. You know the Sub-kingdoms and Classes into which its learned and ingenious author, upon a novel and most remarkable plan, has divided the Animal Kingdom[1444]. I shall now copy for you his diagram of the Annulosa.
ANNULOSA
I have before sufficiently noticed these Classes, or Orders as Mr. MacLeay terms them, of the Sub-kingdom Annulosa: I shall here therefore only throw out a few remarks on their composition. With regard to their circular distribution in the Crustacea, Mr. MacLeay thinks the series runs from the Branchiopods or Monoculus L. to the Decapods or Cancer L.; and so on, till by means perhaps of the genus Bopyrus, which Fabricius regards as a Monoculus, it returns to the Branchiopods again. This circle, through Porcellio, a kind of wood-louse, &c., which has only a pair of antennæ and at first but six legs, is connected with the Ametabola Class, which beginning with Glomeris goes by the other Chilognatha (Iulus L.), having also six legs at first, and certain Vermes to the Anoplura, and terminates in the Chilopoda (Scolopendra L.) their cognate tribe[1445]. From the Ametabola Mr. MacLeay proceeds to the Mandibulata, between which two groups he has discovered no osculant one, but he takes the Anoplura of the former as the transit to the Coleoptera in the latter; from whence passing to the Orthoptera, &c., he finally returns by the Hymenoptera. Between the Mandibulata likewise and Haustellata he finds no osculant class: but as the affinity between the Trichoptera and Lepidoptera is evident, proceeding by the Homoptera he returns to the Lepidoptera by certain Diptera, as Psychoda, &c. From the Aptera Lam. or Pulex L. he passes by the osculant class Nycteribida to the Arachnida; and beginning with the Acaridea, he goes to the Scorpionidea, and so to the Aranidea or spiders, which he connects with the Decapod Crustacea;—thus forming his great circle of five smaller ones, each of which, as well as that which they form, returns into itself[1446].
We next take his Circles of Mandibulata: thus—
MANDIBULATA