48 CLAUDE FULLER. 



issue from the stem just where the dorsals enter the head 

 cavity. They have the appearance of having grown together 

 in the embryo, and after anastomosing, one becomes arrested, 

 the other extends forwards and crosses and anastomoses with 

 an out-curved, ti'ansverse commissure which connects the two 

 dorsals. This problematic development results in the arrange- 

 ment found at birth, as illustrated by iig. 21c (PI. IV). 

 The change of appearance that results later, fig. 21b, is no 

 doubt due to the strain of structural developments, and these 

 draw the middle trachea into a position which is approxi- 

 mately in the longitudinal axis of the head. 



VI. THE TRACHEA OF THE WING-SAC, THEIR 

 GENESIS AND GROWTH. 



Via. The Trachea. 



The tracheae of the wing-sac are outgrowths from those 

 sections of the spiracular trunks lying within the meso- and 

 metathorax, and, with two minor exceptions, they have been 

 found to originate between the bases of the Y-shaped trachea? 

 of the second and third pair of legs, fig. 48 (PI. V). The 

 outstanding exception to this rule occurs in T. natalensis. 

 In this insect the base of the post-costal is frequently beyond 

 that of the anterior arm of the leg-trachea. In Hodotermes 

 viator it was once found similarly situated, but in this species 

 the post-costal is less frequently independent of the radial 

 than it is in T. natalensis. The rule holds good for the 

 local representatives of the following genera that have been 

 examined: Hodotermes, Calotermes, Cryptotermes, 

 Rhinotermes, Microtermes, Eutermes, Hamitermes, 

 Cubitermes, Procubitermes, Promirotermes, and 

 Microcerotermes. The tracheae have either two or three 

 connection-. In the representatives of the generaCalotermes, 

 Cryptotermes, Eutermes, Hamitermes, Cubitermes, 

 Procubitermes, Pro miro termes, and Microcerotermes 

 there are regula'ly three. To these connections with the 

 cardinal stem it is proposed to apply the terms radial root. 



