BREEDING TECHNIQUE 345 



receptacle containing the food. The tin frame is then covered with a 

 closely fitting bag made of wide-meshed mosquito netting, which is tied 

 with a strong tape some distance belo\v the mouth of the jar ; the upper 

 end of the bag is closed with a purse string. As the flies hatch out of 

 the pupae they rest on the mosquito netting. 



About six hours after most of the flies have hatched out they should 

 be given some food, either sterilized goat's spleen or sugar and water ; 

 the spleen is sterilized as follows : It is heated svhen intact in 

 a bunsen flame for about one minute, so that all bacteria which may be 

 on the surface are destroyed. It is then placed in a sterile petri dish 

 and cut up into small pieces with a sterile knife. One of the pieces is 

 then passed through the flame to still further ensure its sterility as far as 

 any surface organisms are concerned, and is placed in a receptacle 

 which consists of an ordinary watch glass which has been sterilized and 

 then fixed to a light tin frame ; it is suspended in the glass jar containing 

 the flies by hooking it to the netting. During hot weather it is neces- 

 sary to keep the piece of spleen moist, and this is done by mixing a 

 small quantity of sterile water or saline solution with it. Fresh spleen 

 should be given every eight to twelve hours. The sugar and water can 

 be put into the receptacle while it is in the cage with a glass pipette ; it 

 should be changed regularly and not allowed to ferment. Dead flies can 

 be taken out of the jar by first removing the food receptacle and then 

 tipping up the jar and picking them off with a pair of forceps. 



In order to obtain strong healthy flies it is most important to feed the 

 larvae regularly ; if this is not done they pupate prematurely and the flies 

 which hatch out later are short lived. 



If for any reason it is not possible to obtain the eggs of a species of 

 Mitsca in the way described above, the flies should be liberated in one of 

 the large cages (Plate XLIV, fig. 4), at the bottom of which a quantity 

 of fresh horse dung is placed in a tin tray ; if the flies are given some food, 

 either spleen or sugar and water, they will oviposit in the dung. 



Horse dung, though an excellent food for the larvae of Musca nebulo 

 has one serious disadvantage, in that it is frequently infected, at least in 

 Madras, with the embryos of a species of Oxyuris, probably O. curvula, 

 Rud. The larvae ingest them with their food and the worms undergo 

 their development in the puparia, so that when the flies emerge, they are 

 heavily infected with the adult stage. Infected flies soon die, since 

 they are unable to feed ; their proboscides are rendered rigid by the large 

 collection of mature worms. In Madras horse dung as a food for the 

 larvae of Mitsca nebulo had to be abandoned, and instead the contents 

 44 



