THE CHEESE-HOPPER 115 



mechanics of the cheese-hopper's leap still await complete 

 elucidation. 



A very similar, if not identical fly devours the fat of 

 salt hams, and is sometimes very destructive. 



In April the grubs sought to leave the moist cheese, and 

 to find dry hiding-places. It was surprising to see how 

 they were able to flatten their bodies in their efforts to 

 squeeze through narrow chinks. When they had gained 

 suitable retreats, they ceased to move, and the skin, lately 

 so flexible, turned hard, changed from white to red, and 

 glistened like burnished copper. The shape of the body 

 underwent a change, becoming more regularly cylindrical, 

 though the narrowed head-end, and the thicker, tuber- 

 culate hinder- end could still be distinguished. The cheese- 

 hopper was thus transformed into a hard, shining, motion- 

 less, seed-like pupa. Within the larval skin, which was 

 not cast, but retained as an outer wall of defence, a new 

 skin, the pupal skin, formed, and within this were de- 

 veloped the new organs of the fly, infinitely more complex 

 than those which sufficed for the unadventurous larva. 



In May the flies began to emerge ; at the head-end the 

 segments split open horizontally, and a singular object 

 protruded, which was recognised as the head of the fly. 

 From the forehead projected a great bladder, which 

 fluctuated as the pressure within rose and sank. It is by 

 means of this bladder that the fly forces open its prison- 

 walls (see p. 19). Next the legs and wings were extri- 

 cated, which adhered, not to the hard outer case, but to 

 the flexible pupal skin within. When it first becomes free, 

 the fly is soft, pale-coloured, and unable to use its wings, 

 which look like crumpled white appendages of the thorax. 

 They are slowly extended until they project considerably 

 beyond the end of the abdomen, assuming gradually the 

 gauzy texture and the iridescent colours of nearly all 

 transparent insect- wings. Meanwhile the brownish-grey 

 of the body changes to a shining, metallic black. The 

 fully formed fly is only 5 mm. (} in.) long, much smaller 



