72 HOW TO COLLECT 



aqueous solution of perchloride of mercury, 1 in 500. Other 

 specimens of the same species sliould be pinned and labelled with 

 a reference to those in spirit, so that the latter may be identified. 



Killing. 

 Diptera brought back alive after a day's collecting should be killed 

 by being placed for a few minutes in the closed cyanide- bottle or jar. 

 If the cyanide-jar is sufficiently large, the pill-boxes themselves may 

 be placed therein, first opening them a fraction of an inch on one 

 side to allow the cyanide to take effect. In the case of large sluggish 

 Diptera, such as Strat'iomys, the pill-box may be opened without 

 fear of the insect effecting its escape ; after which a smart tap on 

 the bottom of the box will cause the fly to drop into the jar. 

 Diptera should never be allowed to remain exposed to the effects 

 of the cyanide longer than is necessary to ensure their being quite 

 dead. If the poison is of reasonable strength, four or five minutes 

 should be sufficient to kill even the largest and strongest flies ; on 

 the other hand, it is necessary to make sure that the insects are 

 really dead, since, if the exposure to cyanide has been too short, flies 

 will often appear to be dead when in reality they are only stupefied. 

 As soon as the insects are really dead, they should be removed from 

 the killiug-jar ; those in pill-boxes may be allowed to remain therein 

 until one is ready to pin them, while the loose specimens should be 

 turned out on to a sheet of cork-carpet or pith. 



Methods of preserving Diptera other than by pinning. 



Diptera should always he pinned, and this should be done as soon 

 as they are dead. If preserved in any other way, they will never 

 make such satisfactory specimens. 



When, however, it is impossible to pin them, Diptera may be 

 preserved in fine sawdust, on which a few drops of dilute carbolic 

 acid should be sprinkled to prevent mould. Each specimen, before 

 being placed in the sawdust, should be loosely screwed up in fine 

 tissue-paper (cigarette-paper would do), on which the necessary data 

 (see below under " Pinning ") should be written in pencil. To contain 

 the specimens a small tin box (such as those in which tobacco is sold) 

 should be used ; and to prevent injury from shaking, the box should 

 be packed quite full of sawdust and specimens, 



