Fig. 207.—Alimentary canal and appendages of the mole-cricket: a, head; b, salivary glands and receptacle; c, lateral pouch; d, stomato-gastric nerves; e, anterior lobes of stomach; f, peculiar organ; g, neck of stomach; h, plicate portion of same; i, rectum; k, lobulate gland; l, extremity of body; m, Malpighian tubes. (After Dufour.)
The alimentary canal and digestive system of Gryllotalpa present peculiarities worthy of notice. Salivary glands and reservoirs are present; the oesophagus is elongate, and has on one side a peculiar large pouch (Fig. 207, c); beyond this is the gizzard, which is embraced by two lobes of the stomach. This latter organ is, beyond the lobes, continued backwards as a neck, which subsequently becomes larger and rugose-plicate. On the neck of the stomach there is a pair of branching organs, which Dufour considered to be peculiar to the mole-cricket, and compared to a spleen or pancreas. The single tube into which the Malpighian tubules open is seated near the commencement of the small intestine. These tubules are very fine, and are about one hundred in number. The arrangement by which the Malpighian tubules open into a common duct instead of into the intestine itself appears to be characteristic of the Gryllidae, but is said to occur also in Ephippigera, a genus of Locustidae. According to Leydig[[262]] and Schindler the Malpighian tubules are of two kinds, differing in colour, and, according to Leydig, in contents and histological structure. Near the posterior extremity of the rectum there is a lobulated gland having a reservoir connected with it; this is the chief source of the foetid secretion the mole-cricket emits when seized. The nervous chain consists of three thoracic and four abdominal ganglia; these latter do not extend to the extremity of the body; the three anterior of the four ganglia are but small, the terminal one being much larger.
The number of eggs deposited by a female mole-cricket is large, varying, it is said, from 200 to 400. The mother watches over them carefully, and when they are hatched, which occurs in a period of from three to four weeks after their deposition, she supplies the young with food till their first moult; after this occurs they disperse, and begin to form burrows for themselves.
It has been said that the young are devoured by their parents, and some writers have gone so far as to say that 90 per cent of the progeny are thus disposed of. M. Decaux, who has paid considerable attention to the economy of the mole-cricket,[[263]] acquits the mother of such an offence, but admits that the male commits it. The number of eggs in one nest is said to be about 300.
The embryonic development of the mole-cricket has been studied by Dohrn[[264]] and Korotneff,[[265]] and is considered by the former to be of great interest. The tracheae connected with each stigma remain isolated, while, according to Korotneff, the development of the alimentary canal is not completed when the young mole-cricket is hatched. Perhaps it may be this condition of the digestive organs that necessitates the unusual care the mother bestows on her young.
Fig. 208.—Cylindrodes kochi. Australia. A, outline of the Insect with five of the legs and the extremity of the body mutilated; B, middle leg. (After de Saussure.)
The genus Cylindrodes (Fig. 208, C. kochi) comprises some curious and rare Insects of elongate, slender form. They are natives of Australia, where the first species known of the genus was found in Melville Island by Major Campbell, from whom we learn that these Insects burrow in the stems of plants, and are so destructive that he was unable to keep a single plant in his greenhouse on account of the ravages of Cylindrodes campbellii. The form of these Insects is beautifully adapted to their habits, the body being contracted in the middle in such a way as to permit the middle and hind legs to be packed against it, so that the cylindrical form is not interfered with by these appendages while the excavating anterior legs are at work in front of the Insect. The abdomen has nine segments; the terminal one, said to be remarkably long and destitute of cerci, is not shown in our figure.
The genus Tridactylus is considered by de Saussure to form, with its ally Rhipipteryx, a division of Gryllotalpinae, but they are treated, perhaps more correctly, by Brunner as a separate tribe. T. variegatus (Fig. 209) is a small Insect, abundant in sandy places on the banks of rivers in Southern Europe,—extending on the Rhone as far north as Geneva,—and is remarkable for its great power of leaping, and for the rapidity with which it can burrow in the sand. This anomalous Insect has only ten joints to the antennae. Its alar organs are imperfect, and not like those of other Gryllidae in either form or neuration. The hind legs are of peculiar structure, the tibiae terminating in two processes between which is situate a rudimentary tarsus. Near the extremity of the tibia there are some plates, forming two series, that can be adpressed to the tibia, or extended as shown in our figure. The body is terminated by four rather short, very mobile processes; the upper pair of these are each two-jointed, and are thought by de Saussure and Haase[[266]] to be cerci; the inferior pair, being articulated processes of the anal segment, their presence in addition to cerci is remarkable. It is difficult to distinguish the sexes of this Insect.
