Cuénot, L. Études physiologiques sur les Orthoptères. (Arch. Biol., xiv, 1895, pp. 293–341, 2 Pls.)
Needham, James G. The digestive epithelium of dragon-fly nymphs. (Zool. Bull., i, 1897, Chicago, pp. 104–113, 10 Figs.)
With the writings of Mingazzini (see p. 323), Kowalevsky, Ranvier, Haidenhain, Beauregard (p. 323), Sadones.
THE GLANDULAR AND EXCRETORY APPENDAGES OF THE DIGESTIVE CANAL
Into each primary division of the digestive canal open important glands. The salivary and silk-glands are offshoots of the œsophagus (stomodæum); the cœcal appendages open into the stomach (mesenteron), while the urinary tubes grow out in embryonic life from the primitive intestine (proctodæum), and there are other small glands which are connected with the end of the hind-intestine.
a. The salivary glands
We will begin our account of these glands with those of the Orthoptera, where they are well developed. In the cockroach a large salivary gland and accompanying reservoir lie on each side of the œsophagus and crop. The gland is a thin, leaf-like, lobulated mass, divided into two principal lobes. These open into a common trunk, which after receiving a branch from a small accessory lobe, and from the salivary reservoir, unites with its fellow to form the unpaired salivary duct which opens into the under side of the lingua. Each salivary reservoir is a large oval sac with transparent walls. (Miall and Denny, also Figs. 299, sr, and 327.) The ducts and reservoirs have a chitinous lining, and the ducts are, like the tracheæ, surrounded by a so-called spiral thread, or by separate, incomplete, hooplike bands, which serve to keep the duct permanently distended. In the locust (Fig. 298) the lobules are more scattered, forming small separate groups of acinose glands. In the embryo of Forficula Heymons has observed a pair of salivary glands opening on the inner angle of the mandibles, a second pair opening in the second maxillæ, while a third pair of glands, whose function is doubtful, is situated in the hinder part of the head, opening to the right and left on the chitinous plate (postgula) behind the submentum. In Perla, there are two pairs segmentally arranged (Fig. 343).
Fig. 323.—Left side of the head of the silkworm: a, adductor muscle of the mandible, from which the muscular fibres have been removed; b, upper fibres of the same; c, lower fibres cut away to show the adductor muscle (e); d, fibres inserted on the accessory adductor lamella; f, œsophagus, much swollen; g, salivary gland; h, dorsal vessel; i, l, tracheæ of the mandibular muscles; k, trachea; n, optic nerve.—After Blanc.
