12 STRUCTURE OF CERTAIN DIPTEROUS LARV^. 



LIFE HISTORY. 



The life history of these flies presents many remarkable and 

 peculiar phenomena. The females of a number of them deposit eggs 

 which hatch, and the larva pursues the normal line of development. 

 With other species the larva hatches within the body of the parent 

 and is deposited in the fu'st stage or sometimes in the second or even 

 third stage. In Mesemhnna the larva is deposited in the second 

 stage, in Dasyphora in the third stage. Upon what food the larva 

 develops within the body of the parent is not yet known; Port- 

 chinski thought that they might feed on undeveloped eggs which he 

 observed near the larvjr. It seems difficult, however, to believe this 

 possible. In the allied tsetse flies the larva, when deposited, is fully 

 grown. The various stages of larval development at deposition serve 

 to lessen the difl'erences between the Pupipara and other Diptera. 



In the number of eggs deposited these flies vary greatly, some 

 species, like Musca corrina, Myospila ineditabundn , and Mesembrina 

 mystacea, deposit only 24 eggs or less; these, however, are quite 

 large. PyreUia and Orapliomyia lay about 50 eggs; Musca domestica 

 and Cynomyia deposit between 100 and 200 smaller eggs, while Calli- 

 phora erytlwoce pTiala lays from 400 to 600 eggs, all extremely small. 



Siniilarily those larvae deposited alive var}^ in number and size. 

 Hylemyia strigosa deposits but one or two large larvfie in the first stage, 

 while Soirophaga hsematodes deposits 40 to 60 smaller larvae. 



After deposition there is sometimes a variance in development. In 

 Musca domestica there are the usual three larval stages; the first with 

 a heart-shaped aperture to the posterior sjnracles, the second with 

 two slits, and the third with three winding slits. In the allied 

 Myospila meditahunda, according to Portchinski, the eggs are much 

 larger and fewer in number than in the house fly, the larA'a upon 

 hatching has the usual simple heart-shaped aperture to the posterior 

 spiracles, but from this first stage the larva transforms directly to 

 the third stage with three slits in each stigmal plate, thus omitting 

 the second stage. This enables the fly to pass through all stages 

 quickly, and to breed during hot weather and in small patches of 

 manure that are apt to dry up too quickly for use by some other flies. 



Portchinski has shown that the coprophagous habit induces 

 viviparity. Mesemhrinu meridiana is coprophagous and viviparous; 

 the other species, Mesembrina resplendens, lays eggs and is not 

 coprophtigous. The coprophagous Dasyplwra pratorum is vivip- 

 arous, while D. hsiophth a] ma lays eggs; Hylemyia strigosa is coproph- 

 agous and viviparous, while most other species of the genus deposit 

 eggs. 



Portchinski also claims that the same species may vary in these 

 habits; according to him Musca corvina in northern Russia la3's 



