HABITS OF TWO PARASITES OF BLOW- FLIES. 



227 



observation made at 10.15 a.m. the same day s])Owed that the act 

 reqnii'ed 8 minutes ; the host pup;irium was that of Mnsca 

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

 into pnparia of the Phonnia at 9.32 A.M. and 1,20 p.m. the same 

 day. One confined at 10 a.m. tlie same date with two pnparia of 

 tlie same liost oviposited at once." (6.) 



The position of insertion of the ovipositor is very variable. 

 Any segment laterally, dorsally, or ventrally is attacked, in 

 captivity. 



One female may insei t lier ovipositor more than once in the 

 same pnparium. One pnpaiinm may be attacked by several 

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

 same time. 



Length of Feriod of Ovvposition. — When amply supplied with 

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

 first g'eneration from material obtained from Reijent's Paik 

 were still actively at work, whilst their own progeny were 

 emerging and had begun attacking hosts. 



Time elapsing between Emergence and Prod.uction. — When host 

 pnpa.ria are available, oviposition takes [)lace 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 })y 

 a female varies. "In three instances one female [)la,ced in a, tube 

 with fifteen pupa^ parasitized the whole, with t!ie exception of 

 two pupa3 which ha<l 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 from each pupa varied 

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



In the case of two females each confined separately with liost 

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

 progeny numbered 21 males. 57 females, total 78, and 38 males, 

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

 the second 22 (6). 



Fartlieno genesis. — "On September 27th, 1908, 12 virgin females 

 of hrevicornis, reared separately fiom [)uparia, of Fliorrnia regina 

 and in no instance accessible to males, were confined separately, 

 each in a small gelatine capsule with a. single known healthy 

 pnparium 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 tlie larva3 of the parasites were 

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

 parasite is parthenogenetic." (6.) 



Proportion of the Sexes. — Under this heading Girault and 

 Saunders tabulate 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 ; tliese were from puparia collected " from a 

 single host lot from a decomposecl cadaver, city dumping- 



Proc. Zool, Soc — 1920, No. XVI. 16 



