[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.
[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 Poduræ 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.
[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.
[12] Lubbock considers that Papirius should be placed in a distinct family from Smynthurus, because it wants tracheæ. Their presence or absence scarcely seems to us to be a family character, as they are wanting in the Poduridæ, and are not essential to the life of these animals, while in other respects Papirius seems to differ but slightly from Smynthurus.
[13] Dr. Laboulbène has recently, and we think with good reason, separated Anura maritima from the genus Anura, under the name of Anurida maritima.
[14] Memoirs of the Peabody Academy of Science, II. Embryological Studies on Diplax, Perithemis, and the Thysanurus genus Isotoma. Salem, 1871.
[15] Translated in 1859 by Mr. Dallas under the title "Facts for Darwin."
[16] "Whether that common stem-form of all the Tracheata [Insects, Myriopods and Spiders] which I have called Protracheata in my 'General Morphology' has developed directly from the true Annelides (Cœlminthes), or, the next thing to this (zunachst), out of Zoea-form Crustacea (Zoepoda), will be hereafter established only through a sufficient knowledge and comparison of the structure and mode of growth of the Tracheata, Crustacea and Annelides. In either case is the root of the Tracheata, as also of the Crustacea, to be sought in the group of the true jointed worms (Annelides, Gephyrea and Rotatoria." He considers the first insect to have appeared after the Silurian period, viz., in the Devonian.
[17] The Zoëa is born with eight pairs of jointed appendages belonging to the head, and with no thoracic limbs, while in insects there are but four pairs of cephalic appendages and three pairs of legs. Correlated with this difference is the entirely different mode of grouping the body segments, the head and thorax being united into one region in the crab, but separate in the insects, the body being as a rule divided into a head, thorax and abdomen, while these regions are much less distinctly marked in the crabs, and liable in the different orders to great variations. The great differences between the Crustacea and insects are noticeable at an early period in the egg.