SOUTH AFEICAN TERMITES. 51 



become tubei'cles which arc almost regularly clavate, fig-. 52, 

 but in other species they are conical, fig. 53. It is during 

 the development of the buds into the tubercle form that the 

 extensions of the meso- and metathorax become noticeable. 

 With the first marked extension a scape grows from each 

 tubercle, and very frequently on one side of its apex, fig. 54. 

 These three scapes (or stalks) extend into the Aving-sac as 

 simple trachea and are the radial, medial, and cubital 

 ti-acheae ; the differentiation between the basal tubercle and 

 its scape soon disappearing. In Termes, Odontotermes, 

 and Microtermes (and presumably Hodotermes) the 

 cubital tubercle early assumes a bifid foi-m and two stalks 

 grow from it, fig. 55. 



In Calotermes and Cryptotermes it has been observed 

 that before the differentiation between scape and tubercle 

 takes place, a secondary tubercle forms near the base of the 

 radial, fig. 56, and from this develops the post-costal trachea. 

 At this stage four simple tracheas occur in the wing-sac. Soon 

 after the post-costal has developed a little, the vermiform bud 

 of the sub-costal appears upon the radial stem, fig. 57, and 

 this grows into a stalk, so providing the wing-sac with five 

 trachege. Still later, the anal issues from the root of the 

 cubital, fig. 58, so that there are six simple tracheae, fig. 59. 

 Not until all have made some growth does any one produce 

 branches. 



VIc. The Growth and Development of the Wing-Sac 



Trachej*:. 

 From the foregoing account it will be gathered that the 

 tracheas of the wing-sac arise in an orderly sequence. Those 

 first appearing are the ones which normally develop the 

 strongest ; that is to say, where there are three roots, the 

 strongest tracheee are the radial, the medial, and the cubital, 

 and, where there are two roots, the strongest are the radial 

 and the duplicated cubital. 



For Calotermes and Cryptotermes, the preliminary 

 development may be summarised as follows : 



4* 



