SOUTH AFRICAN TERMITES. 53 



origin makes no diffei'ence to the regular behaviour seen in 

 the wings of more mature nymphs. In all cases, on entering 

 the wing-sac it approaclies tlu^ radial. In the hind wing it is 

 briefly applied to the radial, bending back again to a median 

 position ; in the fore it does not reach to the radial, but 

 recedes and becomes briefly applied to the cubital, from which 

 it bends off again to a median position. 



This trait may be taken as evidence that, where there are 

 two basal connections, the base of the medial trachea has 

 migrated to the base of the cubital ; but against this is the 

 evidence furnished by the frequent duplication of trachese in 

 Calotermes and the frequent occurrence of a true indepen- 

 dent medial, in the presence of a duplicated cubital^ 

 in Microtermes incertus. Moreover, in Hodotermes, 

 Termes, Odontotermes, and Microtermes both stems 

 of the cubital develop along similar lines ; a simihirity of 

 development which is most marked in Hodotermes and 

 T e r m e s . 



The subsequent development of the wing trachese comprises 

 the following : 



(j) The production of main branches — ^or offsets.^ 



(^•) The growth, from stems and offsets, of inniimerable- 

 tracheal fibrils. 



In the last nymphal instar the wing-sacs are pervaded with 

 trachese — especially those of the more generalised species — 

 and it is by no means uncommon for the principals and their 

 sub-divisions to extend and travel — usually in the dii-ection of 

 the base of the wing-sac — along the edge of the marginal 

 thickening, figs. 78, 94 (PI. VII) ; these extensions may also 

 bend back into the body of the wing-sac, fig. 142 (PI. IX). 



Apart from the normal, many cases of apparently abnormal 

 development have beeu noticed ; that is to say, a principal 

 trachea is often duplicated. 



^ It is convenient to apply the term "offset " to the regular series of 

 main branches of the cubitus exhibited by all species, and also to the 

 series of outer branches of the radius possessed by Hodotermes,. 

 Calotermes, and Cryptotermes. 



