The information that exists as to the internal anatomy of {360}Termites is imperfect, and refers, moreover, to different species; it would appear that considerable diversity exists in many respects, but on this point it would be premature to generalise. What we know as to the respiratory system is chiefly due to F. Müller.[285] The number of spiracles is ten; Hagen says three thoracic and seven abdominal, Müller two thoracic and eight abdominal. In fertile queens there usually exist only six abdominal stigmata. There is good reason for supposing that the respiratory system undergoes much change correlative with the development of the individual; it has been suggested that the supply of tracheae to the sexual organs is deficient where there is arrest of development of the latter. The alimentary canal is only of moderate length. Salivary glands exist, as also do salivary reservoirs; these latter are large, in some species remarkably so. The oesophagus is slender, but abruptly enlarged behind to form a large crop; a proventriculus is apparently either present or absent; the chylific ventricle, or stomach, is slender and simple. The Malpighian tubules are very long; their number is probably from four to eight in the adult, and in the earlier stages less. Behind the tubes the alimentary canal forms a large paunch, and after this there is a small intestine and rectum. The paunch is a peculiar structure, and probably of great importance in the economy of Termites. These creatures emit minute quantities of a secretion that is corrosive, and can act on metal and even glass;[286] its nature and source are not understood. Hagen describes peculiar structures in the rectum to which he is inclined[287] to ascribe the origin of this substance, but this is very uncertain. [Illustration: FIG. 229.—Head and alimentary canal of _Termes lucifugus_ (nymph). _a_, head; _b_, salivary glands; _c_, salivary receptacles; _d_, crop; _e_, stomach; _f_, intestinal paunch; _g_, small, _h_, large intestine; _i_, Malpighian tubes; _k_, extremity of body. (After Dufour.)] The brain is small; the infra-oesophageal ganglion is placed {361}immediately under the supra-oesophageal; there are three thoracic and six abdominal ganglia. The nervous system apparently differs but little in the various forms, or in the different stages of life, except that in the fertile females the abdominal ganglia become so much enlarged that they even exceed the brain in size. The testes are unusually simple; each consists of eight capsules opening into the vas deferens; the two vasa converge and are continued as a short ejaculatory duct; at the point of convergence there is a pair of curled vesiculae seminales.