50 CLAUDE FULLER. 



regard as the post-costal, the radial, and the cubital. The 

 post-costal is a shortened trachea whose position is analogous 

 to one of the two independent phases of this trachea in T . 

 natalensis. The radial is a simple trachea with a few weak 

 outer branches. The cubital is a duplicated trachea as in 

 Termes, Hodotermes, Odontotermes, Microtermes, 

 and abnormally in Calotermes. Occasionally the cubital 

 root carries three tracheas and the more anterior of these 

 may be regarded as the medial trachea (see figs. 165, 166 

 (PI. X), and discussion. Section IXd). 



VIb. The Gtenesis of the Wing-sac Tracked. 

 Plate VI, figs. 49-59. 



In any adult termite, the two pairs of equally diaphanous 

 wings extend, when folded, to about the same point. In 

 other words, the hind wings are shorter to a fixed degree 

 than the fore wings. This condition is achieved by the 

 earlier appearance of the fore wings; and it is frequently 

 possible to detect two phases of tracheal growth in the 

 organs of one insect, the tracheee of the fore wings being 

 slightly older they are usually a little more advanced in 

 growth than those of the hind. Much that is said in this and 

 the next subsection rests upon this circumstance, as, naturally, 

 it has not been possible to examine the continuous develop- 

 ment of the wing tracheae in one insect. 



The lateral extension of the meso- and metathorax — the 

 beginning of wing-growth — takes place when the insects are 

 very young, about 1'5 to 2 mm. in length. In Crypto - 

 termes, in particular, the genesis of the tracheae seems to 

 occur before there is any obvious lateral extension. The 

 sections of the spiracular trunk first bulge outwards, and, 

 having assumed this position, buds arise, fig. 51 (PI. VI), and 

 soon develop into tubercles. In Cry ptotermes^ the buds 



' The account from here onwards of growth of tracheae refers in par- 

 ticular to this generalised species, and to Calotermes durbanensis; 

 any jioint at which a more specialised species differs is the subject of 

 special remark. 



