DIPTERA OR TRUE FLIES. 



243 



usually placed in groups of two, three, or four, close to- 

 gether, each egg being sculptured hexagonally. In a week 

 or ten days they hatch into small white maggots, which 



Fia. 138.— Mangold Fly (Pegomym beta'). 



1 and 2, Male, nat. size, and mag. ; 3 and 4, female, nat. .size, and mag. : 

 larva, nat. size, and mag. ; 7 and 8, puparium, nat. size, and mag. 



5 and 6, 



burrow into the soft mesophyll layers of the leaf : there these 

 footless grubs live for four weeks, forming first a small pale- 

 green patch, which gradually grows into a white and then 

 brown blister. When held up to the light the maggots can 



Fig. 139. — A, Ova of Mangold Fly (Pegomyia ietcc), and b, adult. 



be seen within. On reaching maturity they mostly fall out 

 to the ground, where, as in all this group of flies, the skin of 

 the larva hardens and forms a brown puparium, as soon as the 

 larva has pushed its way an inch or two under the soil. In 



