484 Annals of the South African Museum. 



series derived from many nests and localities should be studied before 

 attempting to make innovations in the classification. It is frequently 

 the case that the $ $ of the first brood differ not only in size but also 

 in minor details of structure from those of later broods, and I am 

 inclined to believe that not a few new races and varieties have been 

 erected on such slender foundations. 



In the separation of the species the following points should be noted: 

 The pro-mesonotal suture, although usually more or less effaced in 

 the middle, can generally be traced by a depression which becomes 

 deeper at the sides and is often angular in form. At the apex, or 

 a little behind the apex of the mesonotum, there is in many species 

 a longitudinal median tubercle or carinula. It is of some diagnostic 

 value, but as it is liable to variation in the degree of prominence and 

 length, even within the species, too much reliance should not be placed 

 on it. The epinotal spines are similarly variable within the limits of 

 a species, and a great deal too much importance has been attached to 

 the comparative length of those structures in the separation of the 

 species. The mesonotum has a declivous face behind, just above 

 the meso-epinotal suture. This face is usually much shorter than the 

 anterior and more or less horizontal face; it is sometimes concave 

 transversely, and its lateral margins are sometimes defined by sharp 

 raised edges or carinulae. The length of the declivity and its degree 

 of obliquity are characters of diagnostic value and fairly reliable. 

 The 1st joint of the petiole is nearly always thicker (from above to 

 below) behind than in front, and seen from above is generally of a 

 trapezoidal or triangular form, the apex of the triangle truncate and 

 invaginating the short and globose peduncle of the 2nd joint. In 

 measurements of these two joints the length of the 1st should be 

 taken from the level of its anterior angles to the level of the point 

 behind where it touches the anterior margin of the node of the 2nd 

 joint; the length of the 2nd joint should be taken over the node 

 only, since the short peduncle in front is telescoped into the 1st joint 

 to a variable depth and can rarely be seen in its entirety (see Text- 

 fig. 31). Owing to the peculiar mode of attachment of the petiole, 

 which is articulated to the base of the dorsal plate of the abdomen, 

 the latter can be carried reflected over the thorax, and this atti- 

 tude is assumed when the insect is alarmed, but in some species that 

 position of the abdomen is adopted without any apparent provocation, 

 more especially when the insect is moving head downwards on a 

 vertical or steep plane. 



From the anal glands a sticky whitish fluid of an unpleasant odour 

 is secreted, which is freely exuded when the ants are disturbed. 



