THE EXTERNAL STRUCTURE OF ANTS. 15 



in its embryonic development through a stage in which the body con- 

 sists of twenty like, or homonomous segments. Six of these belong 

 morphologically to the head, three to the thorax and the remaining 

 eleven to the abdomen. The first and third segments bear no appen- 

 dages, the second bears the antennae, the three thoracic segments bear 

 the three pairs of legs, and the second and third of these segments in 

 the males and females develop, at a much later stage, the two pairs of 

 wings. The first abdominal, which has long been known as the 

 media ry segment, becomes fused with the hind portion of the third 

 thoracic segment during pupal development, as Janet and Emery have 

 demonstrated, and becomes the epinotum of the latter author. The 

 pedicel consists of the second abdominal segment, or of this and the 

 third segment, while the remaining seven or eight form the gaster. 



The Integument. The chitinous investment, or integument varies 

 greatly in thickness in the different species of ants, being very hard and 

 brittle in many of the more primitive groups (Ponerinaa, Myrmicinse, 

 Dolichoderus, Pol\rhachis) and thinner and more pliable in the more 

 recently developed forms (most Dolichoclerime and Camponotinae). 

 The microscopic character of the integument is of considerable impor- 

 tance to the taxonomist, especially in the more delicate discrimination 

 of geographical subspecies and varieties and may be considered under 

 the captions of sculpture, pilosity, pubescence and color. These all 

 present a bewildering variety of modifications. In some ants the sur- 

 face of the body is very glabrous and shining, in others opaque, punc- 

 tate, foveolate, rugulose, rugose, tuberculate, striate or reticulate, and 

 these sculptural characters may be combined in the most diverse pat- 

 terns. The term pilosity applies to the longer, reclinate, erect or 

 suberect hairs, the term pubescence to the minute, appressed tomentum, 

 which may cover the whole or portions of the body and appendages. 

 Both the hairs and pubescence vary greatly in length and density or 

 abundance, and the former may be tapering and pointed, straight, 

 flexuous, or hooked, obtuse or clavate, or dilated and flattened to form 

 scales. 



No doubt all of these differentiations in sculpture, pilosity and 

 pubescence are correlated with the delicate tactile sense of the ants. 

 Certainly one who has examined many species of ants will have no 

 difficulty in understanding why these blind or nearly blind insects seem 

 to display such keen delight in palpating with their antennae and bur- 

 nishing with their tongues the exquisitely chased or chiselled armor of 

 their fellows. In some ants the hairs may be specialized for particular 

 functions on certain portions of the body. I find this to be the case, 

 for example, in several genera of desert ants (Fig. 2), which have the 



