THE ORDER DIPTERA 



43 



The pupa of the house-fly is an example of a coarctate 

 pupa; that of the mosquito is an example of an obtected 

 pupa. 



In some flies (e.g. Sinmliunt, Fig. 33), the pupa is 

 enclosed in a silky cocoon which is spun by the larva as 

 a preliminary to pupation. 



The mature fly, or imago, escapes from the pupal shell 

 or the puparium in one of two ways. In the case of the 

 coarctate pupa the anterior end of the puparium is usually 

 pushed off by a distensible bladder-like sac, known as the 

 ptilinum (? tttIXov = a. plume), which protrudes like a hernia 

 from the " forehead," or front, of the emerging fly (Fig. 9). 



Junule 



puparium 



Fig. 9. — Blow-fly emerging from Pupal Case. 



Jabel/um 



Fig. 10.— Muscid Head. 



When the fly has crawled out of the ruptured puparium the 

 ptilinum shrivels, and is ultimately retracted into the head 

 of the fly ; but a record of its existence is left in the form 

 of a crescent-shaped scar, known as the frontal lunule (Fig. 

 10), which embraces the roots of the antennae. Where the 

 distension of the ptilinum has been great, the ends of the 

 frontal lunule are produced far down the face on either side 

 of the antennae, these extensions of the scar being known 

 as \k\e frontal suture (Fig. 10). 



In the case of the free or obtected pupa the pupal skin 

 is split either longitudinally down the back, or in a T-shaped 

 fashion, or transversely, and the fly withdraws itself much 

 as a hand is withdrawn from a glove. 



