HABITS OF TWO PARASITES OF BLOW-FLIES. 217 



(7) 11 to 14 days; Froggatt (8) 15 days. Under laboratory 

 conditions with a mean temperature of 20° C. it was found to 

 average 21 days. 



The Egg. — The egg is translucent white, with a smooth glossy 

 surface, cylindrical, slightly tapering to one extremity and 

 broadly rounded at both ends (text-fig. 13). The newly- deposited 

 egg measures from -30 to '35 mm. in length and -11 to -14 mm. 

 wide at broadest part (8). The eggs are placed in clusters under 

 the shell of the puparium and upon the surface of the pupal 

 integument of the developing fly, the latter occasionally being 

 punctured by the ovipositor. They are found in clusters of 



Text-figure 13. 



Egg of N. hrevicornis, 26 hours old. Size '125 X '350 mm. 

 X41. Original. 



2 to 12 or more or singly, and ar^e situated on any pait of the fly- 

 nymph, but are commonly found in the depression of the 

 junction of head and thorax, or thorax and abdomen. " The eggs 

 appear to be coated with a trace of some sticky substance, which 

 causes them to adhere together, and to the covering integument 

 of the fly-pup?e "' (8). The egg undergoes a slight increase in 

 size as the development of the embryo progresses. The duration 

 of the egg-stage varies considerably ; those observed ranged from 

 30 to 74 hours. 



The Larva. — Immediateh" upon hatching, the young larvse start 

 feeding. They punctin-e the pupal skin of the host with their 

 mandibles, and with these firmly attached to the enveloping skin 

 of the pupa, proceed to absorb the body-fluids of their host. 

 They remain about the same position until full-grown. As the 

 larvte develop, the host is gradually absorbed, and consequently 

 shrinks inversely to the growth of larvse. " As a rule, the 

 remains of a pai^asitised host — the fully-formed pupa — is a flat, 

 scale-like mass, apparently consisting of the ventral shell of the 

 pupa and that of the head ; for example, the thec?e of the eyes, 

 legs, and wings are discernible, and the remains are not much 

 shrunken so far as the original length is concerned. In the 

 case of Cynomyia cadavernia, in one puparium infested with 

 21 larvfe of the first spring generation the parasites were all 

 attached to the dorsal surface of the host from the pronotum to 

 the tip of the abdomen ; these parasitic larvas were nearly full- 

 grown. But in another puparium of the same host, in which 

 13 larvae were found, their attachment to the host appeared to 

 be haphazard, and the host-pupa was considerably shrunken, 

 especially in width " (6). No evidence of larval ]3reda,ceousness is 

 foi-thcoming, although dead larvse are frequently found ; thes«* 



