704 Mr. T. H. Taylor on 



the old cuticle from its body, the tracheae, which are 

 attached to it by means of initial threads are at the same 

 time withdrawn through the new spiracles. To permit 

 of this separation of the old tracheal system from the 

 body, the tracheal trunks break across at certain points, 

 which have a segmental arrangement. These tracheal 

 junctions occur immediately posterior to the origin 

 of the ventral segmental branches. At this point the 

 spiral thickening of the intima is wanting. Junctions 

 also occur on the transverse commissures. Two thick- 

 ened annuli of chitin in the centre of the commissure 

 replace the spiral intima, and the commissure snaps across 

 between them. The withdrawal of the old tracheae through 

 the narrow opening afforded by the spiracle no doubt 

 serves to squeeze the air from the old trachese into the 

 new ones. Some air is, however, left sticking to the old 

 collapsed trachese, as an examination of cast larval skins 

 readily shows. 



The spiracles are simple oval thickenings of the cuticle, 

 and conspicuous from their black colour. The two thoracic 

 and seven abdominal spiracles can be readily seen on the 

 surface of the body with a low power. The mesothoracic 

 spiracle is the largest of the series ; the collapsed tracheae 

 which are pulled out through this spiracle from the head 

 and thorax are much more numerous than those which 

 are withdrawn from any of the other spiracles. 



The traclieal system of the pupa (fig. 3) is modelled on 

 that of the larva. The longitudinal trunks are connected by 

 three transverse commissures in the thorax (fig. *3, d). Each 

 trunk gives off in the abdominal segments 1 — 7 a ventral 

 segmental branch, which divides into an ascending and a 

 descending trachea. At their point of separation a slender 

 initial thread passes to the anterior margin of the segment 

 near which the spiracle is situated. The initial threads, 

 like those of the larva, are solid and devoid of spiral 

 markings. The spiracles are simply depressions of the 

 skin. The spiracle of the first abdoiiunal segment is 

 concealed beneath the Aving-sheath. 



In the thorax the two pairs of spiracles have doubtless 

 the same position as they have in the larva, but proof is 

 difficult to obtain. The metathoracic spiracle is concealed 

 beneath the wing-sheath. It is a wide, funnel-shaped 

 depression of tlie cuticle, and is connected with the spiracle- 

 chamber by means of a short thick initial thread. The 



