SOUTH AFRICAN TERMITES. 37 



a 



those travelling- to the dorsal region lightly shaded. Fig. 19 

 shows a side view from below, and is also drawn from 

 cleared preparation of the head of a newly-hatched nymph ; 

 in this figure the trachea3 of the parts upon the further side 

 of the head are omitted. It also illustrates the linking up of 

 the cephalic with the bod}^ system. 



Vc. The Spiracles. 

 Plate V, figs. 22a-45b. 



The spiracles or sti<rmata of an insect are defined as open- 

 ings in the body- wall through which the air passes into the 

 tracheae. Such as are permanently open are regarded as the 

 more primitive or generalised and those with lips as secondary 

 or more specialised. In the case of both types, any occluding- 

 apparatus that may occur is said to be internal; e. g. a piece 

 of mechanism intervening between spiracle and tracheal 

 pipe. In all the species that I have examined such bivalvular 

 types as have been met with have the valves partly external 

 and partly internal, one folding slightly over the other to 

 close the orifice. Moreover, when abdominal, such spiracles 

 are but modifications of an occluding apparatus which formerly 

 (in the nymphal stages) intervened between a fixed opening, 

 or pore, and the pipe. For this reason it is proposed to refer 

 to the apparatus from pore to trachea as the " spiracle,^^ 

 whatever condition it may be in ; and the remarks, upon the 

 structure, mechanism, and development which follow, relate 

 to Term es natalensis Haviland, unless otherwise stated. 



As the greater interest attaches to the abdominal series, the 

 spiracles of the thorax have not been examined with particular 

 attention. It may be said of them that they exhibit a simple 

 bilabial form in the nymph and have no remarkable meta- 

 morphosis. In the adult the first pair is smaller and different 

 from the second, the latter being shaped like a pair of 

 buttocks. Both retain something of their labial form, 

 figs. oSa, b, c (PI. V). They are, however, valvular and 



