2974 THE JOINTED ANIMALS 



Without entering into the more minute details of structure, the general char- 

 acteristics by which the order may be distinguished are as follows: The possession 

 of four transparent wings, a head, thorax, and abdomen distinct from each other, 

 the latter joined to the thorax by a narrow stalk, or, in the case of the Tenthredinidce 

 by a broad uniting joint. The integuments are strong, hard, shiny, and often 

 hairy. The mandibles are well developed for biting purposes, while the subordinate 

 mouth parts are, in the case of the honeybees, modified to form a long tongue-like 

 proboscis for extracting nectar from flowers. The head is more or less globular, 

 bearing compound eyes and several ocelli on the crown between and just behind the 

 antennae. The mandibles are used, besides the mastication of food, for digging 

 holes in the ground or for gnawing timber and various other purposes. In some 

 ants the soldiers have the head enormously developed, as are also the mandibles; 

 their function being to protect the society from enemies, and also to carry on war 

 against neighboring communities. The antennas are in most cases long, jointed, 

 and filiform, constituting sensitive organs of touch and recognition. The thorax is 

 composed of the usual three pieces, prothorax, mesothorax, and metathorax. It 

 bears the wings, four in number, above, and the legs, six in number, beneath, the 

 latter being modified in many species for special purposes, such as, in the bees, for 

 gathering pollen from the blossoms of the plants visited for the sake of honey. 

 Often the legs are armed with long spines, which in the sand wasps materially assist 

 in the excavation of the pits in which these insects bury their victims and deposit 

 their eggs. The wings are ample, strong, and light, formed of a transparent mem- 

 brane strengthened with fine nervures or veins. The arrangement of these nervures 

 varies much in different groups, and is of importance in the classification of mem- 

 bers of the order. The relative importance of this characteristic is, however, not 

 the same in every family, being in the sawflies, perhaps, of the greatest value. 

 Species which are wingless in one or both sexes are found in many of the families; 

 while in the genus Oxyura of the family Proctotrypidce the wings consist merely of a 

 fine central stalk with a battledoor-shaped plumose tip. The abdomen is united to 

 the metathorax either throughout its whole width, as in the Tenthredinidce, or, as 

 in most other families, by a narrow stalk or petiole. These two characteristics serve 

 for the division of the order into the groups of Sessiliventres and Petiolata. The 

 organs of reproduction are situated at the apex of the abdomen; while in the female 

 the instrument for depositing the eggs has become in the section Aculeata developed 

 into a sting; in the Ichneumonidce it is sometimes enormously long, and used for 

 piercing the larvae in which they lay their eggs. In the case of the large wood 

 borers (Sirex] it is used as a boring instrument, while in the sawflies it is serrated 

 on the edges and employed to wound the tender shoots on which the eggs are de- 

 posited. Among the Pompilidce and some other families, the sting is used to par- 

 alyze the victim in which the insects lay their eggs, or leave in the cell to feed the 

 larvae as they hatch. Probably no pain is given to the victim, and even in the case 

 of those grubs that feed internally upon the tissues of caterpillars in all probability 

 less inconvenience is caused than we suppose. 



In all cases the metamorphosis is complete. The egg may be laid in a cell pre- 

 pared either by the female or the workers for the purpose, and the grub is fed by 



