260 JOHN L. FROGGATT. 



Kerosene tins have been used as receptacles for containing the liver during the 

 development of the fly larvae, as these are easily procurable and also cheap. About 

 4 to 5 inches of fine earth sifted through one-tenth inch mesh wire gauze are placed 

 in the bottom of the tin, and the liver, well slashed with a knife, is then placed on 

 the earth. The earth in the tin serves two purposes : — It absorbs the putrefactive 

 juices from the liver which, if allowed to accumulate, would drown the maggots ; 

 and it also forms a clean dry place for the larvae to crawl into when they have finished 

 feeding and have left the remains of the liver. Should the liver appear to be becoming 

 moist on the top, or should the earth underneath become wet before the larvae have 

 reached maturity, more dry sifted earth must be added. The greatest care and 

 attention is paid to this portion of the work ; otherwise the mortality amongst the 

 larvae would be very high. As soon as the majority of the larvae have crawled into 

 the dry earth the remains of the liver are transferred to another tin and the larvae 

 are separated from the more or less damp earth. It is here that the value of the 

 sifted earth is seen, for it affords a rapid separation by allowing the maggots to be 

 sifted without too much knocking about, a happening to be most carefully avoided 

 at all times. The larvae, together with any dirt that will not pass through the sieve, 

 are then placed in a flat shallow pentagonal tray, the apex of the pentagon being 

 cut off to form a narrow opening. The trays are made of tin. The open end 

 should be placed away from the light and the material in the tray stirred about or 

 spread out in a thin layer. The larvae will crawl out and away from the fight, 

 falling into oblong tins containing dry sifted earth which are placed under the 

 open end of the tray. These oblong tins (about 12 inches by 8 inches by 

 3£ inches high) should be kept covered with wire gauze, to prevent insects and 

 mice from destroying the larvae or pupae. Amongst the insects that have to be 

 thus contended with are : — Dermestes cadaverinus (skin beetle), Creophilus 

 erythrocephalus (devil's coach-horse), Saprinus laetus (shining histerid) and 

 Necrobia rufipes (red-legged ham beetle). 



The method of separating the pupae from the larvae is similar to that for separating 

 the larvae from the earth in the breeding tins. The larvae and pupae are sifted out 

 and placed in the sorting trays ; the larvae will crawl away and the pupae will be left 

 behind. By using the trays several lots can be separated at the same time and with 

 little or no rough handling of either the larvae or pupae. 



A matter which is most important, but for which as yet no reason can be assigned, 

 is the fact that occasionally a very large percentage of the fly pupae atrophy, the 

 pupal fly rotting and finally drying up. It was thought in the early stages of these 

 investigations that this might have been caused by damage done to the maggots 

 or pupae during sorting, for our methods were not so much simplified as they are now ; 

 but still even now it is found to occur. Furthermore, on a number of occasions 

 deaths of pupae from this cause have been observed in the field where the carcases 

 have never been disturbed. 



It is generally amongst the pupae of Pycnosoma rufifacies, and to a lesser extent 

 P. varipes, that this species of Chalcid wasp is found actually at work in the field. 

 This is largely due to the habits of the larvae of these two species, which do not crawl 

 away from a carcase to pupate unless the remains have been much disturbed, but 

 pupate either just under the edge of the remains or else affix themselves to the bones, 



