42 CLAUDE FULLER. 



spiracle. Fig. 32 represents spiracle III and figs. 33 and 34 

 show the form of spiracles IV to X of the female and illus- 

 trate the reduction of the lever. 



In hg. 32 the resister {B.) is reduced and to it is attached the 

 visceral edge of the trachelos {m. tr.) and it still performs its 

 original function of closing against the much modified but 

 strongly developed lever (L.), behind which the trachea is seen. 

 The chin-plate (C) is fixed in the cuticle of the body-wall. 

 The occluding muscle [oc. m.) still extends from it to the lever 

 and the extensor muscle {ex. m.) to the margin of the tergite. 



The spiracles of the queen, being more of the nature of 

 tracheal development, are dealt with in the next section, 

 Vd. The condition seems due to the great distension of the 

 conjunctiva, but this does not explain it wholly, as the 

 tearing away does not occur in other queens, which enlarge 

 considerably. The elongate depressions that result have 

 many pits in them, like ear-holes, and into these many trachea? 

 open freel3^ 



Vd. Tracheal Growth aistd Modifications. - 



Considered apart from the cardinal stem of the respiratory 

 system, the growth and development of trachea? is tree-like. 

 A trachea grows indeterminately or with a marked tendency 

 to dichotomise. It sends out branches which behave similarly. 

 As the branches increase in length and number, the stem 

 enlarges as does the trunk of a tree. In their ramifications 

 the tracheal course is, on the whole, like that of a root in the 

 soil; with most, however, the field of growth is controlled and 

 a particular region is invaded, but the detail of movement 

 appeal's ungoverned. This is illustrated by the arborescent 

 branches of the dorsal-longitudinal trachea in fig. 12 (PI. Ill), 

 and in the branching of the leg-tracheas, fig. 39 (PI. V). 



One of the outstanding developments occurs in the case of 

 the pipes of the abdominal spiracles of the female. These 

 are originally simple tubes subdivided into three, as described 

 in Section Va. As the nymph develops, a great number of 



