BREEDING TECHNIQUE 305 



of dead weeds, or any other decaying matter which is likely to render the 

 water very foul. If fifty larvae are placed in each tray, and they are well 

 scattered, about one-fifth will reach maturity. At this stage they remain 

 in a resting condition without feeding, and should be removed from the 

 tray and placed singly in the small jam jars (Plate XLIV, fig. 5) ; each 

 jar should have a good screw top, well perforated with holes just small 

 enough to prevent the larva from getting out. The jar should contain 

 sufficient moist mud to enable the larva to bury itself; the mud should 

 be changed once a week. The removal of the old mud is accomplished 

 by filling the jar about half full of water, and stirring up the mixture with 

 a glass rod until it is sufficiently fluid ; it is then turned out over a 

 coarse sieve, which catches the larva but permits the fluid to pass through. 

 The larvae should not be picked up with forceps, and it is well not to 

 touch them with the fingers, as they are capable of inflicting a sharp bite 

 with their powerful mandibles. 



In due course the larvae pupate, and are then found just at the 

 surface of the mud and almost completely covered, at most their dor- 

 sal surfaces being exposed. It will be remembered that the imago 

 emerges out of the pupal case through a T-shaped slit on the dorsal 

 surface of the thorax, and the pupa lies in such a position that this can 

 be accomplished without any accident. The pupae should be removed 

 from the jars in the same way as the larvae, and placed in small holes 

 in moist mud in one of the cages, which is covered with a good 

 net. If the pupa is held by its anterior end and the last abdo- 

 minal segment inserted just in the hole, it will soon wriggle itself 

 into the desired position. A little flag with all the data relating 

 to the particular pupa should be fixed in the mud close to it. The 

 pupae should be kept under observation in order to secure the flies as 

 they hatch out. If some of the larvae are left in the tray and allowed 

 to pupate, the pupae will be found some distance from the water ; it is 

 not, however, advisable to leave the pupae in a tray containing larvae, as 

 they are often killed. 



Attention to all these details is very necessary, for these flies, 

 more than any others, require careful handling, or the worker 

 will find that though he began with 500 larvae, he will end with 

 one or two flies. The secret of success in this work largely lies 

 in obtaining as near as possible the natural surroundings of the 

 larvae, and in order to do this it is essential to study the habits of 

 the flies and to note exactly where, and under what conditions, they 

 lay their eggs. 

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