[74] Palmén cites one striking proof of the low position of Ephemeridæ among Insects. Their reproductive outlets are paired and separate, as in Worms and Crustacea.
[75] These examples are cited by Palmén.
[76] Eaton, Trans. Ent. Soc., 1868, p. 281; Vayssière, Ann. Sci. Nat., Zool., 1882, p. 91.
[77] Zur Morphologie des Tracheensystems (1877).
[78] We take these instances from Eaton, Monograph of Ephemeridæ, Linn. Trans., 1883, p. 15.
[79] Charles Brongniart has lately described a fossil Insect from the Coal Measures of Commentry, which he names Corydaloides Scudderi, and refers to the Pseudo-Neuroptera. In this Insect every ring of the abdomen carries laminæ, upon which the ramified tracheæ can still be made out by the naked eye. Stigmata co-existed with these tracheal gills. (Bull. Soc. Sci. Nat. de Rouen, 1885.)
Some Crustacea are furnished with respiratory leaflets, curiously like those of Tracheates, with which, however, they have no genetic connection. In Isopod Crustacea the exopodites of the anterior abdominal segments often form opercula, which protect the succeeding limbs. In the terrestrial Isopods, Porcellio and Armadillo, these opercula contain ramified air-tubes, which open externally, and much resemble tracheæ. The anterior abdominal appendages of Tylus are provided with air-chambers, each lodging brush-like bundles of air-tubes, which open to the outer air. Lamellæ, projecting inwards from the sides of the abdominal segments, incompletely cover in the hinder part of the ventral surface of the abdomen, and protect the modified appendages. (Milne Edwards, Hist. Nat. des Crustacés, Vol. III.)
[80] Gerstaecker has found in the two first abdominal segments of Corydia carunculigera (Blattariæ) pleural appendages, which are hollow and capable of protrusion. They have no relation to the stigmata, which are present in the same segments, and their function is quite unknown. See Arch. f. Naturg., 1861, p. 107.
[81] Jointed cerci are commonly found in Orthoptera (including Pseudo-Neuroptera); in the Earwig they become modified and form the forceps. The “caudal filaments” of Apus are curiously like cerci.
The cerci are concealed in the American Cryptocercus, Scudd. (Fam. Panesthidæ).