DIPTERA. 
67 
feeding upon the meat, rapidly grow until they reach maturity and pass into the 
pupa stage. Many persons believe that blue-bottles are full-grown examples 
of the house-fly, and when informed that such is not the case, and that these 
insects after reaching the winged stage are incapable of growth, point out that 
blue-bottles vary greatly in size, and ask what may be the explanation of the 
difference. The answer is, that the size of the blue-bottle in its final stage depends 
upon the size of the maggot before pupating, and the size of the maggot upon 
the amount of nourishment it is able to obtain before its supply of food was 
exhausted. In any given case, when the supply is limited, the maggots that 
are the first to hatch will get more food than those that appear later, and 
in consequence, when the whole of it is exhausted, will have attained a greater 
length and fatness than the others, and thus become converted into larger flies. Or, 
GROUP OF FLIES AND THEIR GRUBS. 
1, Blow-fly ; 2, Eggs ; 3, Larvie ; 4, Pupa; 5, Newly-born larva of grey flesh-fly; 6, Grey flesh-fly : 7, Adult-larva 
of the same ; 8, House-fly and larva; 9, Sharp-mouthed fly ; 10, Head of house-fly ; 11, Foot of grey flesh- 
fly ; 12, Carcase of house-fly killed by fungus growth. (10, 11, enlarged ; the other nat. size.) 
again, if three or four hundred eggs be laid in a dead mouse and the same number 
in a dead rabbit, it is clear that in the former case the supply of food will be 
smaller for each larva, and will sooner come to an end than in the latter. 
The grey flesh-fly (Slarcophaga carnaria) is a handsome species, measuring in 
the female half an inch in length. Seldom entering houses, it is not uncommon 
in the open country, where it may be seen basking in the hot sun upon stones 
or walls. Its prevailing colour is pale slate-grey, variegated on the thorax with 
black bands, and the abdomen with square black spots, set corner to corner like 
the squares of a chess-board. A noteworthy fact connected witli this species is 
that the eggs hatch within the parent before being laid, so that the young arc 
born alive; the}’ feed upon decaying animal and vegetable matter. The blow¬ 
flies belonging to the genera Galliphora and Lucilia, respectively known as 
the blue-bottle and green-bottle flies, as a general rule deposit their eggs upon 
dead animal matter. This, however, is by no means always the case, there being 
many instances on record of the laying and hatching of the eggs upon living 
