Pupa— Imago 1 2 1 



whence it has separated, and hardening, becomes 

 transformed into a protective pupa-case or piiparium 



(fig- 79)- 



Breathing of the Pupa. — The puparium, how- 

 ever, remains connected with the enclosed pupa by 

 air-tubes, through which breathing can be carried on, 

 and the thoracic spiracles, useless during the larval 

 stage (fig. 68 b) now become functional. The 

 devices for enabling insects to breathe during the 

 pupal stage are very varied. Pupae to which the free 

 air can get access breathe by means of their abdominal 

 spiracles, whether they are suspended in the open or 

 buried in an earthen cell. Pupae which live submerged 

 in water necessarily have the spiracles closed. Some 

 breathe the dissolved air by means of gill filaments ; 

 the aquatic pupce of Midges are provided with tufted or 

 branching filaments in connection with the air-trunks 

 of the first thoracic segment. Others — those of Gnats 

 for instance (fig. 72 b) — breathe through a pair of 

 stout tubes (" respiratory trumpets"), also on the first 

 thoracic segment, the upper extremities of the tubes 

 remaining in contact with the surface film of the 

 water as the pupa floats about (170). Similar re- 

 spiratory trumpets on one or two segments of the 

 body also serve to convey air to pupie, like those of 

 many flies, which are buried in mud or foul refuse. 



Formation of the Imago. — As those insects 

 which pass gradually from the nymph to the perfect 

 state assume by degrees the wings and other outward 

 characters of the adult, a correspondingly slow and 

 gradual process of change goes on internally, the 

 most important feature being the maturing of the 

 organs of generation. In insects which undergo a 

 complete metamorphosis the reproductive organs also 

 slowly mature through larval and pupal life, while 

 the nervous system becomes gradually modified by 



