HABITS OF TWO PARASITES OF BLOW-FLIES. 227 



observation made at 10.15 A.M. the same day showed that the act 

 veqnired 8 minutes ; the host puparium was that of Musca 

 domestica; .... A female confined at 9.20 a.m., Sept. 10, deposited 

 into pnparia of the Phormia at 9.32 a.m. and 1.20 p.m. the same 

 day. One coniined at 10 a.m. the sa.me date witli two pupavia of 

 the same host oviposited at once." (6.) 



The position of insertion of the ovipositor is very variable. 

 Any segment laterally, dorsal!}', or vcntrally is attacked, in 

 captivity. 



One female may inseit her ovipositor more than once in the 

 same puparinm. One pnparium may be attacked by several 

 females in turn ; sometimes two will be seen at work at the 

 same time. 



Length of Period of Oviposltion. — When ampl}' supplied with 

 host pnparia, the females appear to live from 3-4 weeks. The 

 iirst generation from material obtained from Regent's Park 

 were still actively at work, whilst their own progeny were 

 emei'ging and had begun attacking hosts. 



Time elapsing hetiveen Emergence and Production. — When host 

 puparia ai'e available, oviposition takes place within a, few hours. 

 In three specific instances observed by Girault and Saunders 

 oviposition took place in 24, 10^, and 3 hours after emergence. 



Progeny of Single Females. — The number of eggs deposited by 

 a female varies. "In tliree instances one female pla,ced in a tube 

 with fifteen puppe pa,rasitized the whole, with the .exception of 

 two pup?e which had decayed. The total number developing 

 from the one parasite in the first case was 140, in the second 148, 

 and .the third 96. (The numbers emerging fi-om each pupa varied 

 from 15 to 1 in these experiments.) " (8.) 



In the case of two females each confined separately with host 

 puparia, the first with 130, the second witli 86, their respective 

 progeny numbered 21 males, 57 females, total 78, a,nd 38 males, 

 65 females, total 103. The first female parasitized 17 puparia, 

 the second 22 (6). 



Parthenogenesis. — "On September 27tli, 1908, 12 virgin females 

 of brevicornis, reared separately from puparia. of Phomvia regina 

 and in no instance accessible to males, w-ere confined sepaiately, 

 each in a small gelatine capsule with a single known healthy 

 puparium of Phormia ; on September 29th at 11.30 a.m., in three 

 cases females were observed ovipositing ; on October 15th, 1908, 

 the progeny of two of the virgin females emerged as follows : — 



17 males .... and 15 males Other emergences did not 



occur, but in three instances the larvfe of the parasites were 

 found in the host puparia, all dying, however. Hence tliis 

 parasite is parthenogenetic." (6.) 



Proportion of the Sexes. — Under this heading Girault and 

 Saunders tabula.te the numbers and .sexes of 7369 specimens dealt 

 with by them. In lot No. 3 (of this table) they bred 710 males 

 and 786 females ; these were from pupai'ia collected " from a 

 single host lot from a decomposed cadaver, cit}^ dumping- 



Proc. Zool, See— 1920, No, XVI. 16 



