344 MEDICAL ENTOMOLOGY 



himself as to whether he is dealing with one or more than one species of 

 Musca ; the imagines can be submitted later to an expert for identifi- 

 cation. 



Having cleared the ground by the above experiment the eggs of the 

 species to be used can be obtained every day or every other day accord- 

 ing to the number of flies required. As before the eggs should be 

 placed on fresh horse dung, and the jar kept daily in the sun for a short 

 time. About twenty -four hours after the larvae hatch out it is neces- 

 sary to give them fresh dung and at the same time to remove that 

 which has been used up. This is carried out by first disturbing the 

 superficial layers of the dung with a pair of forceps, turning them over 

 several times ; as a result the larvae, which are generally at the top, at 

 once pass down to the lower part of the dung. The upper layers can 

 now be removed without losing any of the larvae, and fresh dung is 

 added. In a very short time the larvae return to the fresh food, and if 

 it is daily added to the jar in the way described growth takes place with 

 extraordinary rapidity, and by the fourth or fifth day they will be ready 

 to migrate preparatory to pupating. At this stage they begin to crawl 

 up the sides of the jar, and it will be noted that there is no food 

 visible in their alimentary tracts, an indication that they are ready to 

 pupate. The jar should be placed in the mud enclosure as before and 

 before leaving the laboratory the cloth cover should be removed. The 

 larvae crawl out of the jar during the night and bury themselves in the 

 sand, where they pupate. If the jar is not placed in the enclosure, but 

 is left standing on a table, the larvae will force their way through the 

 cloth covering, and, dropping on the floor, crawl into cracks or crevices 

 in order to pupate. From extensive experience it has been found that 

 this is the only satisfactory way of breeding Musca nebulo in large 

 numbers. The larvae as they crawl out of the glass jar into the sand 

 at the bottom of the enclosure bury themselves in it and never crawl 

 up the mud walls of the enclosure. 



When most of the larvae have pupated, the pupae should be removed, 

 and if necessary washed, and then placed at the bottom of one of the 

 glass jars ; a tin frame made as follows is now attached to the jar (Plate 

 XLIV, fig. 5). A long strip of tin about 1 inch in width is soldered 

 together at the ends so as to fit closely over the mouth of the jar. At 

 convenient distances apart four similar strips of tin are soldered to the 

 frame, and at the other end they are soldered to a circular piece of 

 tin which has a large hole cut out of its centre, and over which is fitted 

 a tin lid. This upper opening is necessary in order to insert the 



