HABITS OF TWO PARASITES OF BLOW-FLIES. 201 



naked eye. It is translucent white, with a smooth glossy surface. 

 The time required for the egg to hatch varies, and in an investi- 

 gation into this point active first iustar larvfe were found in the 

 hosts, which had pupated 66 hours after the eggs were deposited, 

 the temperature during this time being 20° C. But, that the 

 egg hatches in from 30 to 50 hours generally is obvious from the 

 condition of the host pupa, which is either in a state of histo- 

 lysis or an early stage of histogenesis ; and also by the occasional 

 distorted appearance of the host puparium. The egg is deposited 

 in any part of .the larval host, and this lack of discrimination 

 accounts for the non-appearance of the paiasite on occasions. If, 

 for instance, the egg was lodged amongst muscles, it would be 

 crushed by the movements of the host larva ; this point is 

 mentioned again under Oviposition. 



The Larva. — The first instar larva (text-fig. 2) diflfers in 

 appeai-ance from the later instars, pa.rticulai'ly in the shape and 

 appearance of its head, which is a thickly chitiuized brownish 

 capsule fitted with a stout pair of mandibles, and has a pair of 

 small protuberances on the dorsal surface, the antennae. It 



Text-figure 2. 



First iustar larva of A. manducator. Camera-lucida drawing, parti}' 

 recoiisti'ucted. X41. Original. 



consists, apparentlj', of 14 segments including the head; the 

 abdomen terminates in a " tail "-like appendage, the abdominal 

 vesicle. A similar organ in Microgaster, and other endo-parasitic 

 Hymenoptera, Gatenby (5) concludes is respiratory in function. 

 That this is the function of this organ in A. manducator appears 

 very probable, and it pi'esumably functions by means of osmosis. 



Since the larva sometimes hatches in the body of its larval 

 host before histolysis has begun, its head seems well adapted to 

 enable it to move in the host pupa if it hatches — as it usually 

 does — during the process of histolysis or that of histogenesis. 



What part of the host forms the food of the various instars 

 has not been observed, but it must consist of liquid or semi- 

 liquid, and in the first instar would probably be the body-fluid 

 and fat-bodies ; and the later instars would feed on those 

 systems which have ceased breaking down or building up after 

 the original attack of the first instar larva. That the larva 

 sometimes hatches before the host pupates is evidenced by the 

 fact that a puparium containing the parasite occasionally bears a 



