THE STRUCTURE OF THE BLOW-FLY 137 



The Larva 



The larva, or maggot, hatches out in a day or so from eggs 

 laid in the carcasses of animals. It buries itself in the flesh, 

 feeds voraciously, and grows very fast, attaining its full size in 

 a fortnight or less, when it is a little less than an inch long. 



Observe some live maggots ; they are soft and white, widest 

 behind, and tapering gradually towards the head-end, which is 

 very narrow. The body is apparently divided into eleven 

 segments, though this is probably not the full number. Each 

 segment is roughened at the constrictions which separate it 

 from the next segments by annular bands of minute hooks ; 

 these are used by the footless maggot in crawling ; the rest of 

 the surface is smooth. ^ 



The conical first sag- ^-,,^'-?r^f°r7r5T!"^77— •s^.— tT«<fr^^S'i^ 

 ment, which is the pro- ^^^Scifi-cjl -"fl~'^|J-'^|f^3^^-Vl~'i^^ 

 thorax, encloses the ^~'''^^-^^-<:Ji.;^J|:^\%i^^^^^ 



head; two other thor- 

 acic segments follow, Fig.77.-LarvaofbIow-fly. ^4. 



and there are eight abdominal segments, of which the last 

 probably represents more than one ordinary segment. 



The head is reduced to a vestige, and contains little besides 

 the jaws and their muscles ; it requires to be studied by the 

 microscope. When protruded from the first segment, it exhibits 

 a pair of large rounded lobes, each of which bears two minute 

 prominences, one above the other. Two large chitinous hooks 

 will be found, one on each side of the mouth. In a fresh- 

 hatched larva there also is a large median hook, pladed above 

 the mouth ; this is cast at the first moult. On each side of 

 the mouth, outside the large hooks, is a rounded lobe, marked 

 with radiating lines. There is an internal skeleton to the 

 head, which serves for the attachment of muscles. The brain 

 is not lodged, as in most insects, in the head, but in the 

 metathorax. The great simplification and reduction in size 

 of the larval head may be attributed (i) to the ease with 

 which the food is procured, leading to degeneration of the 

 mouth-parts and sense-organs ; (2) to the retraction of the 

 head into the thorax, a provision not uncommon in burrowing 

 Dipterous larvae, and often associated with a backward dis- 

 placement of the brain, as well as with a notable reduction in 



