92 THE HOUSE FLY— DISEASE CARRIER 



pupariiim. Observations were carried on through suc- 

 ceeding months and the duration of the Hfe cycle was 

 carefully studied (Psyche, February, 1910). The life 

 cycle is longer in the spring and shorter in summer, 

 the average life cycle being twenty-two and one- 

 half days with usual temperature. They found that 

 one female was able to parasitize twenty-two puparia 

 and another one seventeen. The authors suspect that 

 the phenomenon of polyembryony, that is to say, the 

 development of a number of adult individuals from a 

 single egg, takes place with this species. Counts of 

 several thousand reared specimens of the parasite in- 

 dicated that fifty-eight and nineteen-hundredths per 

 cent, of them were female and forty-one and eighty-one- 

 hundredths per cent, were males. They found that the 

 adult parasites issue from the host puparium through 

 from one to three circular holes of various positions, 

 several issuing from each hole. As to the abundance 

 of the parasite, the authors indicate that during Sep- 

 tember and October, 1908, they reared 8,000 or more 

 specimens, and these were reared quite accidentally, that 

 is to say, without conscious effort on their part to in- 

 crease the number. The local abundance of the para- 

 site was indicated by the fact that in a portion of a 

 given experiment the percentage of parasitism was as 

 high as ninety per cent. This percentage of mortality 

 on the part of the house fly, however, was by no means 

 general, and the parasite had apparently concentrated 

 its attack on certain spots. The authors made an un- 

 successful attempt to propagate the species artificially 



