Upwards of one thousand species are assigned to the genus _Mutilla_, which is distributed over the larger part of the world; there is so much difference in these species as to the nervuration of the wings in the males, that several genera would be formed for them were it not that no corresponding distinctions can be detected in the females. Three or four species of _Mutilla_ are described as being apterous in the male as well as in the female sex; they are very rare, and little is known about them. Only three species of Mutillides occur in Britain, and they are but rarely seen, except by those who are acquainted with their {96}habits. The African and East Indian genus, _Apterogyna_, includes some extremely peculiar Hymenoptera; the males have the wing nervuration very much reduced, and the females are very ant-like owing to the deep constriction behind the first abdominal ring. SUB-FAM. 2. THYNNIDES.—_Males and females very different in form; the male winged, the front wing with three, or only two, sub-marginal cells; the female wingless and with the thorax divided into three sub-equal parts._ [Illustration: Fig. 39—_Methoca ichneumonides._ A, Male; B, female. Britain.] The Thynnides are by some entomologists not separated from the Mutillides; but the distinction in the structure of the thorax of the females is very striking. In the Thynnides the nervuration of the wing appears always to extend to the outer margin, and in the Mutillides not to do so. This family is represented in Britain by a single very rare Insect, _Methoca ichneumonides_: to the unskilled observer the female would appear to be without doubt an ant. This Insect is by some considered as the type of a family distinct from the Thynnides proper. Thynnides are numerous in Australia. Very little is really known as to their habits, though it has been stated that they are parasitic on Lepidoptera, Bakewell having obtained specimens from subterranean cocoons of that Order. Those who are interested in differences between the sexes of one species should examine the extraordinary examples of that phenomenon presented by the Thynnides; the dissimilarity throughout the group—which is now of considerable extent—being so extreme that no entomologist would from simple inspection believe the two sexes to have any connection; but the fact that they are so connected has been demonstrated beyond doubt. In very few {97}cases, however, have the sexes been matched, so that at present males are no doubt standing in the lists of Hymenoptera as one species and their females as other species. SUB-FAM. 3. SCOLIIDES.—_Pronotum reaching back to the tegulae; legs stout; intermediate tibiae with one apical spur; both sexes winged; the nervures not extending to the posterior_ (i.e. _distal_) _margin_.