1900.] 39 



transformation approaches, because, first, tlicy get larger and are 

 more readily seen ; and, secondly, they approach the margin of the 

 water and are more easily taken. 



The best rearing device is the one that keeps its inmates under 

 conditions most nearly natural. A cage for aquatic insects that 

 hardly disturbs such conditions at all consists of a cylinder of 

 galvanized wire screen, open at both ends, having a loose screen cover 

 with a rim of heavy wire. One end of the cylinder is pushed down 

 into the mud of the bottom in shallow water, the cover is laid on and 

 all is ready. Such a cage merely incloses a small water area with its 

 natural vegetation, and nymphs placed inside live their natural lives 

 and obtain for themselves their accustomed food. Of course the size 

 of the mesh must be adapted to that of the insects to be reared — 

 small enough to confine them and large enough to admit their prey. 

 Fifteen inches is a convenient height. 



For burrowing nymphs it will be necessary to set the lower edge 

 of the cage down into the mud of the bottom 2 or 3 inches ; this is 

 easiW done with a garden trovv'el. 



It is better, owing to danger from freshets, not to plant such a 

 cage in the rapids in the direct course of a stream, but to divert a 

 small arm of the stream behind some sheltering rock or log, place the 

 cage there and build miniature rocky rapids inside it. In quiet 

 waters no such precautions are necessary, but where the rise and fall 

 of the water level is great it may be necessary to move cages some- 

 times. In general, it is better to hide the cages among vegetation, 

 away from the eyes of the untutored and irreverent. For aquatic 

 insects which pupate on land a cage is easily planted half in the water 

 and half out. 



Nymphs placed inside will readily crawl up the sides to transform. 

 Young images should be taken out as soon as convenient after 

 transformation is completed (otherwise some will fall into the water 

 and die before they are mature) and placed in paper bags with their 

 exuvia? until dry and well coloured. 



Collectors will find it convenient to have cages of this sort made 

 up in " nests " to fit one inside the other, the size of the mesh 

 decreasing with the size of the cage. A nest of a dozen such cages 

 and covers will be found a slight transportation incumbrance. 



One may wish to take nymphs far from their natural habitat and 

 to rear them at home with no streams or ponds near. A simple 

 breeding cage that may be used successfully under such conditions 

 consists of a rough wooden kit, or pail, or tub, or half barrel, with a 



