[Footnote 9: Nicolet, in the "Annales de la Societe Entomologique de France" (tome v, 1847), has given us the most comprehensive essay on the group, though Latreille had previously published an important essay, "De l'Organization Exterieure des Thysanoures" in the "Nouvelles Annales du Museum d'Histoire Naturelle, Paris, 1832," which I have not seen. Gervais has also given a useful account of them in the third volume of "Apteres" of Roret's Suite a Buffion, published in 1844. The Abbe Bourlet, Templeton, Westwood, and Haliday have published important papers on the Thysanura; and Meinert, a Danish naturalist, and Olfers, a German anatomist, have published important papers on the anatomy of the group. In this country Say and Fitch have described less than a dozen species, and the writer has described two American species of Campodea, C. Americana, our common form, and C. Cookei, discovered by Mr. C. Cooke in Mammoth Cave, while Humbert has described in a French scientific journal a species of Jupyx (J. Saussurii) from Mexico.] [Footnote 10: The direct homology of these parts of the head (the occiput and the epicranium) with Perla, Forficula, etc., seems to me the best evidence we could have that the Podurae are not an independent group. In these most fundamental characters they differ widely from the Myriopods. I am not aware that this important relation has been appreciated by observers.] [Footnote 11: As we descend to the soft, tube-like, suctorial (?) mouth of Anura, which is said not to have hard mouth-parts, we see the final point of degradation to which the mouth of the Thysanura is carried. I think that this gradual degradation of the mouth-parts in this group indicates that the appendages in these animals are not formed on an independent type, intermediate, so to speak, between the mandibulate and haustellate types, but are simply a modification (through disuse) of the mandibulate type as seen in Neuropterous insects.] [Footnote 12: Lubbock considers that Papirius should be placed in a distinct family from Smynthurus, because it wants tracheae. Their presence or absence scarcely seems to us to be a family character, as they are wanting in the Poduridae, and are not essential to the life of these animals, while in other respects Papirius seems to differ but slightly from Smynthurus.] [Footnote 13: Dr. Laboulbene has recently, and we think with good reason, separated Anura maritima from the genus Anura, under the name of Anurida maritima.] CHAPTER XIII. HINTS ON THE ANCESTRY OF INSECTS. [Illustration: 177. Pentastoma.] [Illustration: 178. Centipede.]