418 



ARTHROPODA 



The communities of termites and ants are complicated farther by the intro- 

 duction of other insects of various kinds (mostly beetles) as 'guests' or 

 'symphila.' These, together with their young, are fed and cared for by the 

 ants on account of the sweet fluid which they secrete. The ant communities are 

 farther enlarged by other species kept as slaves. In the nests of many tropical 

 termites and ants there are 'mushroom gardens' in the nests, cultures of fungi 

 upon a layer of organic material formed of leaves chewed by the ants. 



The highly developed capacities of these communal insects, their ability 

 to recognize the members of their own colony from the same species of another 

 colony, the working together for the common good, for a long time led to the 

 idea of a high grade of moral and intellectual development, especially in the 

 bees and ants. This view was erroneous. Since the behavior of the animals 

 is much the same when they are separated from their fellows in the pupal stages 

 and are reared so that they have no chance to learn how to work from others, 

 it follows that their acts are innate complex reflexes and are not the result of a 

 conscious education. Yet they have a certain ability to learn, an ability to 

 modify their acts under strange conditions. It is noteworthy that the strikingly 

 similar communities of ants and termites have developed independently of one 

 another, and that the same is true of wasps and bees is shown by the existence 

 of both solitary and social species in both families. 



In the classification four points are of special importance: (i) The seg- 

 mentation of the body; whether the segments of thorax and abdomen follow 

 without change of form, or whether the thorax is sharply marked off from both 

 head and abdomen. (2) The character of the wings, which in the lower forms 

 are either lacking or are delicate chitinous structures, with numerous veins, 

 the wings of the two pairs similar. In the higher forms a degeneration of the 

 wing veins or a leathery consistence of the membrane, together with a divergent 

 development, partial reduction of anterior and posterior wings may occur. 

 (3) The structure of the mouth parts, and (4) the type of 

 development, both described above. With these characters 

 it is easy to differentiate six orders: Lepidoptera, Diptera, 

 Aphaniptera, Rhynchota, Hymenoptera, and Coleoptera. 

 The remaining species were formerly divided among the 

 Orthoptera and Neuroptera, but these groups are not natural 

 and they have been divided into more or fewer groups. Here 

 the Pseudoneuroptera or Archiptera are separated from the 

 Neuroptera, the wingless forms or Apterygota from the 

 Orthoptera. 



Order I. Apterygota. 



At the bottom of the Hexapoda come ametabolous forms 

 which lack wings and which show no evidence of having 

 descended from winged ancestors. They are regarded as 

 slightly modified descendants of the ancestral Hexapod. 

 Besides the lack of wings they show many primitive charac- 

 ters; compound eyes are poorly developed or lacking; the 

 tracheal system degenerate in Collembola consists of 

 isolated tracheal bushes, rarely connected by longitudinal 

 trunks (fig. 437); the mouth parts are biting or piercing, 

 though frequently rudimentary. Especially to be noted is the existence of 

 abdominal appendages, possibly indicating a relationship to certain 'myriapods.' 

 Thus in Scolopendrella (p. 434) there are small stylets on the feet and beside 

 them protrusible sacs. These reappear in the Thysanura and Campodea, and 

 Camapodea has in addition a rudimentary pair of appendages on the first abdom- 



FIG. 463. Lep- 

 isma saccharina* 

 silver fish (after 

 Packard) . 



