XXUI 



INSECTA : DIPTERA 



355 



The Pupa. 



suri'ounds them. When the larva is full grown it is about 

 half an inch long, and two dark spots become visible on the 

 thorax (Fig. 280, B) — a sign that pupation is about to occur. 

 At this time the larva spins a little oval-shaped 

 nest or cocoon, attaching the silk threads on 

 each side to a leaf, and inside this the larval skin is 



thrown off. The pupa retains a 

 good deal of power of movement, 

 and it breaks away one end of 

 the cocoon, so that it finally lies 

 supported in a silken pocket, but 

 with its h€ad-end and branched 



Fia. 281. — Pupae of two species 

 of SimuKum ( x 2). 



tt, Pupal cocoon with a central pro- 

 jection from the upper margin of 

 the pocket ; &, cocoon of Simu- 

 Hum sericeum ; the pupa has 

 four two-branched gill-filaments 

 on each side, and the cocoon is 

 without a central spike. 



nAf.iili. 



Fig. 282. — Pupa of Simuliuw, 

 removed from tlie cocoon. 



respiratory filaments projecting into the current of water 

 (Fig. 281). The pupae in the pockets with a central spike 

 on the margin are like those shown in Fig. 282, having 

 four unbranched filaments on each side, whilst those in the 

 pockets with simple margin, have four two-branched hairs on 

 each side. The pupae are constantly changing their positions 



