EXTERNAL STRUCTURE. 9 



are generally simple, but sometimes toothed or pectinate. The 

 apices of the tibiae are often armed with movable spurs (calcaria), 

 which may be simple in the intermediate and posterior pairs, 

 but if present are always large and pectinate in the anterior ones. 

 These latter are called strigils, and are curved and fringed with 

 bristles on their inner side. Bristles also occur on the metatarsus, 

 opposite to those on the strigil, and the ants clean their antennae 

 by drawing them between these bristles. 



The wings of ants have not been used in classification to the 

 same extent as in other families of the Hymenoptera, chiefly 

 because the workers, which are most often found, are wingless, 

 and the females, which lose their wings after the marriage 

 flight, are more frequently taken in this " deflated " condition ; 

 moreover, the venation of the wings may vary considerably, even 

 in males and females from the same colony. 



The longitudinal veins of the fore-wings have been named by 

 Emery (1913) as follows : 



Costa, subcosta, pterostigma (=stigma Linnaeus), medius, brachius, 

 radius, and cubitus. 



The transverse veins : transversomedialis , basalis (or discoidalis) , 

 first and second cubitalis, and recurrens (or medialis). 



The cells : costal, median, submedian, radial, cubital 1, 2, and 3, 

 discoidal 1 and 2. Not all, however, of these cells and veins actually 

 occur in most British genera (cf. the following figures). 



The Abdomen. 



The abdomen is highly specialized, and in most ants it is sharply 

 divided into a pedicel and gaster. The pedicel may consist of one 

 joint, the petiole, or two joints, the petiole and post-petiole; it is 

 very mobile and is articulated anteriorly to the epinotum and 

 posteriorly to the gaster. When the pedicel is one-jointed it usually 

 consists dorsally of a more or less high scale of variable shape and 

 thickness. 



The petiole is morphologically the second abdominal segment, 

 for actually, as we have seen, the epinotum is the first, and conse- 

 quently the first gastric segment is the third abdominal one. When 

 the pedicel is two- jointed it consists of two nodiform segments, 

 and the first gastric segment is therefore the fourth abdominal one. 



The gaster varies in shape, being round, oval, long, or cordiform, 

 etc., and shows five segments in the worker and female, and six 

 in the male when the pedicel is one-jointed, and four in the worker 

 and female and five in the male, when two-jointed. Morphologic- 

 ally the gaster consists of eight segments when the pedicel is one- 

 jointed and seven when two -jointed ; but the terminal segments 

 are very small and are telescoped into those in front of them. 



In those ants which possess the power of stridulating, the sound- 



