20 ?HE BUTTERFLIES OF THE BRITISH ISLES. 



put on cover and tie it down securely. If brown paper is used, 

 a piece of pasteboard should be put over it and a weight on top 

 of that. Suffocation takes place directly the gas reaches the 

 insect, but it often happens that one or more of the boxes 

 exclude the gas longer than others. At the end of half an hour 

 all may be removed, but the insects will not hurt in any way if 

 left in all night. 



The best kind of boxes for field work are those known as 

 " glass bottomed," as in these the captives can be examined and, 

 if not wanted, may be set free. It is always better to retain 

 only those specimens that we know are really useful, rather 

 than to incur the necessity of throwing away insects after we 

 have deprived them of life. 



If butterflies are pinned on the spot, a collecting box will be 

 required, and the most useful and convenient is one of an oval 

 shape. This should be made of zinc, and lined with 

 cork that is held in place by zinc clips. The cork 

 should be kept damp when in use, and the water used for 

 damping should have a few drops of carbolic acid mixed with it 

 so as to prevent the formation of mould. Insects may remain 

 in such a box for several days without injury. This box will 

 also be useful for relaxing specimens that have been badly 

 set, or have been simply pinned during the busy season. 



In the matter of pins, it is not altogether easy to make 

 suggestions. There are, perhaps, only two makers in this 

 country of entomological pins, and each of these supplies a large 

 number of sizes. The selection of suitable pins will largely 

 depend on the method of setting adopted. Black pins are, 

 however, the best for butterflies, and are now used almost 

 exclusively. 



In pinning a specimen care should be taken that the pin 

 passes in a direct line through the centre of the thorax. Insects 

 that are properly pinned set better, and have a neat appear- 

 ance when arranged in the collection. For regulating the 



