LARVAE AND PUP^E OF DIPTERA 



465 



The larvae of Diptera may be simple maggots with minute 

 heads and no appendages and capable of only limited squirm- 

 ing movements, e.g., the screw- worms (Fig. 250), or they may 

 be quite highly developed, active creatures, e.g., the larvae of 

 mosquitoes, midges, etc. Many are aquatic, many others ter- 

 restrial; usually the eggs are laid in situations where the larvae 

 will find conditions suitable for their development, and the flies 

 often show such highly developed instincts in this respect that 

 it is hard not to credit them with actual forethought. The 

 pupse of the Diptera also vary widely. In one great suborder, 

 Orthorrhapha, the pupa is protected only by its own hardened 



B 



FIG. 209. Types of pupal 

 cases, showing manner of emer- 

 gence of adults. A, empty case 

 of blowfly, typical co-arctate 

 pupa of Cyclorrhapha ; B, empty 

 case of mosquito, typical ob- 

 tected pupa of Orthorrhapha. 



6 



FIG. 210. A, fly emerg- 

 ing from pupal case, show- 

 ing bladder-like ptilinium 

 (ptil.) by means of which 

 the end of the case is 

 pushed off; B, face of fly 

 showing scar or lunule 

 (lun.) left by drying up of 

 ptilinium. (After Alcock.) 



cuticle, and is often capable of considerable activity; from this 

 " obtected " type of pupa (Fig. 209B) the adult insect emerges 

 through a longitudinal slit along the back. In the other sub- 

 order, Cyclorrhapha, the pupa retains the hardened skin of the 

 larva as a protective covering or " puparium," and is usually 

 capable of very slight movement; from this " co-arctate " type 

 of pupa (Fig. 209A) the adult escapes by pushing off the anterior 

 end of the puparium with a hernia-like outgrowth on the front of 

 the head. This outgrowth, called the " ptilinium " (Fig. 210A), 

 shrinks after the fly has emerged, but leaves a permanent cres- 

 cent-shaped mark on the head known as the " frontal lunule " 

 (Fig. 210B) which embraces the bases of the antennae, and gives 



