THE COLLECTION AND PRESERVATION OF DIPTERA S9 



of Paris, are admirably suited in every way (material, ring, 

 and stick) for the collection of Diptera. 



Either one or two killing-bottles (preferably the latter) 

 must be taken into the field, and these should have a wide 

 mouth and be made of good strong glass. They should be 

 about 3 inches in total height, and the bottoms should be 

 charged to a depth of a half to three-quarters of an inch with 

 a mixture of plaster of Paris and cyanide of potassium. It is 

 advisable to put the preparation of such a bottle in the hands 

 of a chemist it is safer and the cost is trifling. Ether and 

 chloroform are sometimes used, but as these are extremely 

 volatile it is necessary to charge the bottles several times 

 during the course of the day, the liquid being dropped upon 

 a piece of cotton-wool or upon small pieces of blotting-paper 

 which may be carried in any ordinary wide-mouthed bottle. 

 This is a troublesome process in the field, and although 

 specimens killed with ether are usually in beautiful condition, 

 the carrying of a supply of the fluid for replenishing purposes 

 is somewhat of a nuisance, while its presence is constantly 

 felt through its penetrating (and to some people sickly) 

 odour. A decided objection to the use of chloroform lies in 

 the fact that flies killed by this medium usually expire in 

 distorted and unnatural positions, with a very undesirable 

 stiffening of the legs and other appendages. It is a great 

 advantage to carry two killing-bottles and to use them 

 alternately, for when the collector is kept busy such a plan 

 ensures a longer closure of each bottle before it is reopened, 

 thus making death certain and avoiding the escape of speci- 

 mens. A number of circular glass-topped boxes should be 

 carried in the pocket or collecting-bag, and it is convenient to 

 have these of the same diameter as the mouths of the killing- 

 bottles, thus facilitating the safe transference of the specimens 

 (especially if there is any wind), which operation should be 

 performed periodically, say every half-hour or so. A 

 third killing-bottle may even be carried for the reception 

 of solitary specimens of more than ordinary interest, 

 and from this extra bottle each specimen should be trans- 

 ferred, as soon as dead, to a separate box. This plan 

 should be followed whenever it is desired to isolate any 



