38 CLAUDE FULLER. 



closed and opened by special muscles. The tracheal pipes of 

 Avhich they are the mouths are united to them by a short 

 tessellated rim and undergo changes in appearance as growth 

 proceeds, changes which do not affect their tracheal character 

 although transforming them into air-reservoirs. The anterioi* 

 reservoirs assume a bottle-shape and the hinder become 

 cordiform. Fig. 22a (PL V) is a sketch of the juvenile con- 

 dition found in M i c r o t e r m e s i n c e r t u s and its development 

 is shown in figs. 22b to E. All the sketches are from indi- 

 viduals of the same species and all except e are drawn to the 

 same scale, e being i-epresented on a smaller scale. The 

 trachea3 shown in part are : 1, the dorsal ; 2, the spiracular 

 of the prothorax and head; 3, the trachea of the first leg; 

 -5, the passage to the second spiracle; and 4 is the venti-al com- 

 missure Avhich issues from the base of 5 to which it is attached 

 on the visceral side of the air-sac. Figs. 22f, g, h represent 

 the development of the pipes of the second spiracles in a less 

 number of stages. The stage shown by 22p accompanies the 

 development shown by figs. 22a, b, c ; 22g accompanies 

 22d ; and H accompanies E, but is drawn on a large scale. 

 The tracheae shown in part are : 1, the passage to the first 

 spiracle ; la, the passage to the third (or first abdominal) 

 spiracle ; 2, the palisade commissure to the dorsal-longi- 

 tudinal ; 3, the ventral commissare. This development 

 applies equally well to that of T. natal en sis. 



Considered as a series, each pair of spiracles may be 

 referred to by a number ; thus the t wo thoracic pairs become 

 I and II and the abdominal eight III to X. Briefly stated, 

 III to X of the winged female of T. natalensis are bival- 

 vular structures which are the final form of the post-embryonic 

 type. III being more advanced than the rest. The bivalvular 

 form of III of the female is only arrived at by III of the 

 winged male ; in this sex the remainder, IV to X, are arrested 

 in a stage closely approaching that exhibited by the whole 

 abdominal series in the nearly mature female nymph. The 

 soldiers and woi^kers display a slightly less advanced form, 

 somewhere between the spiracle of the young and that of the 



