220 MR. A. M. ALTSON ON THE LIFE-HISTORY AND 



The Achdt. — Emergence of the Adult. — "In general, it may be 

 stated that the adult pai-asites emerge from the host pnparium 

 through from 1 to 3 circular holes, situated variously, usually in 

 the dorsal or dorso-lateral aspect ; and when more than one exit- 

 hole, the two or three are usually scattered or widely separated. 

 The manner of emergence does not difl'er for sex. The exit-hole 

 varies in diameter from 0*75 to 1'50 mm. ; it is usually larger and 

 single when the host is Musca or Chrysomyia and smaller when 

 Phormia, though this difference may be more apparent than real. 

 Individual exit-holes may of couise vary considerably in shape; 

 for rarely it may involve the whole of one end of the host 

 puparium, and is then relatively very large and iri'egular. The 

 margins of the exit-holes a,i'e always jagged or serrate, showing 



that the adults gnaw their way out In regard to the time 



of emergence, the males usually emerge from 2 to 20 hours 

 earlier than the females, a, few emerging some hours previous to 

 the simultaneous emergence of the majority, but there is con- 

 siderable variation in individual cases. Thus some males may be 

 the last to emerge, but the tendency is for them to emerge earlier 

 than females." (6.) 



In the laboratory the number of exit-holes was not limited 

 to three, four and five have been seen, and the exit-holes, con- 

 sequently, dorsal, ventral, or lateral (text-fig. 16). 



Text-£eure 16. 



Pupaviiun witli two exit-holes latero-ventrally. N. Irevicornis. 

 Greatly maornified. Original. 



Both sexes emerge with the wings fully expanded. 



Livrvfe have been found in puparia from which — several weeks 

 or months previously — adults had emerged. If this takes place 

 under natural conditions, it would appear that these have very 



