Evaginable organs in the Blattids were first observed by Gerstæcker in both sexes of Corydia; they are yellowish white, covered with hairs, and are thrust out from between the dorsal and ventral plates of the 1st and 2d abdominal segments.
Fig. 359.—Under side of end of Aphlebia, showing the two eversible sacs; V-X, five last abdominal segments; A, portion showing the hairs; B, showing origin of a hair in its follicle.—After Krauss.
In the cockroach (P. orientalis) Minchin detected two pouch-like invaginations of the cuticle, lying close on each side of the middle line of the body between the 5th and 6th tergites of the abdomen. They are lined by a continuation of the cuticle, which forms, within the pouches, numerous stiff, branched, finely pointed bristles, beneath which are a number of glandular epithelial cells. In the male nymph of P. decorata he also found beside these glandular pouches “an additional gland, opening by a tubular duct under the intersegmental membrane between the 5th and 6th terga above the glandular pouch of each side, and extending forward into the body cavity. The gland and its duct are proliferations of the hypodermis, and there is no invagination of the cuticle.” These eversible glands are most complicated in Phyllodromia germanica. While it is absent in the female, in the male it is relatively of enormous size, extending over the 6th and 7th somites, as well as projecting far into the body cavity (Minchin). Haase states that these glands become everted by blood-pressure and give out the well-known disagreeable smell of these insects. He states that in the male of P. germanica the dorsal glands in the 6th and 7th abdominal segments are without hairs and produce an oily secretion; they function as odoriferous organs in sexual union.
In the male of another Blattid (Aphlebia bivittata) of the Canary Islands, Krauss has detected two yellowish dorsal sacs 1.5 mm. in length, opening out on the 7th abdominal segment, and filled full of long yellowish hairs, the ends directed towards the opening, where they form a thick tuft. These eversible glands lined with hairs appear to be closely similar to the long slender eversible hairy appendages or scent organs of certain Arctian and Syntomid moths. (Fig. 359.)
Fig. 360.—External flaps (gl) of glands of Platyzosteria.
We have found the external median wart with lateral lids or flaps in between the 5th and 6th tergites of Platyzosteria ingens Scudder, a large wingless Blattid living under the leaf scars of the cocoanut tree in Southern Florida (Fig. 360), but were unable to detect them in Polyzosteria or in the common Blabera of Cuba, or in another genus from Cordova, Mexico.
In another group of Orthoptera, the Phasmidæ, occur a pair of dorsal prothoracic glands, each opening by a pore and present in both sexes. In the walking-stick, Anisomorpha buprestoides, ♂ and ♀, these openings are situated on each side of the prothorax at its upper anterior extremity, situated at the bottom of a large deep pit. When seized it discharged a “milky white fluid from the pores of the thorax, diffusing a strong odor, in a great measure like that of the common Gnaphalium or life everlasting” (Peale in Say’s American Entomology, i, p. 84). Boll states that the females when captured “spurt from the prothorax, somewhat after the manner of bombardier beetles, a strong vapor, which slightly burnt the skin; when the females were seized by the males a thick fluid oozed from the same spot.” Scudder describes these glands in another Phasmid (Autolyca pallidicornis) as two straight, flattened, ribbon-like bodies, with thick walls, broadly rounded at the end, lying side by side and extending to the hinder end of the mesothorax. In Anisomorpha buprestoides the glands are of the same size and shape (Scudder). In Diapheromera femorata the repugnatorial foramina are very minute, and the apparatus within consists of a pair of small obovate or subfusiform sacs, one on each side of the prothorax, about 1 mm. in length, with a short and very slender duct opening externally at the bottom of the pit (Scudder).
In the Mantidæ these seem to be genuine coxal glands, as there is a pair situated between the coxæ of the first pair of legs. An evaginable organ like a wart, with a glandular appearance, occurs on the hind femora of the Acrydiidæ in a furrow on the under side, into which the tibia fits, about one-fourth from the base (Psyche, iii, p. 32).