858 FRESH-WATER BIOLOGY 



state. Frequently mites may be collected along shore by the use of 

 the pipette, being picked up individually as they swim about 

 in sight. 



The material, if preserved in formalin, may be put aside for future 

 examination. If not, it should be poured soon into a fiat dish, 

 from which the mites may be picked out by means of a pipette. 

 The dish should be looked over several times, as some tend to hide 

 in the debris at the bottom, and stirring after the material has once 

 settled often reveals hidden specimens. 



Five per cent formalin, into which they may be put directly, is 

 likely to make them brittle, and the catch is better preserved in a 

 mixture of glycerine, 2 parts by volume; pure water, 3 parts by vol- 

 ume; 2 per cent acetic acid, 2 parts by volume; absolute alcohol, 

 I part by volume. 



If the mites are to be kept alive for observation their cannibal- 

 istic instincts make it necessary that different genera be segregated 

 and kept in separate dishes, with a small amount of some water 

 plant and a few Crustacea or non-predatory insect larvae as food. 

 Crowding should be guarded against. 



The activity of water-mites makes them difficult objects to study 

 alive, but by the cautious addition of water saturated with chloro- 

 form vapor they may be narcotized, and, after being examined, will 

 come out from under the influence of the chloroform apparently 

 uninjured. The author has subjected specimens to this treatment 

 on several successive occasions without evident harm. 



In the study of specimens it is necessary to make use of slide 

 mounts. The mouth-parts may be dissected and mounted sepa- 

 rately upon sHdes, and the palpi and legs may also be removed and 

 mounted. If the specimens have been kept in a solution contain- 

 ing some glycerine an opening may be made in the body-wall 

 through which the contents of the body can be pressed out, and in 

 that way transparent mounts of the complete individual secured. 

 The thickness of the body makes it difficult to secure a transparent 

 mount from material preserved in alcohol or formalin mixtures, 

 but the specimens may be successfully softened in some cases by a 

 weak potash solution or else must be mounted as opaque objects. 



In the identihcation of water-mites care must be used, as the 



