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Psyche 
[December 
single host. It was possible in the case of E. celtis to check 
the limitation of the mite to the specific host and find that it 
was not adaptable to the host which is affected by what 
would appear to be morphologically a closely related form. 
For a key to the genera of the family and the features 
used in classification one is referred to the work of Nalepa 
or of Hassan. 
Technique 
The importance of reliable permanent preparations and 
the fact that the methods for making permanent collections 
have long been unsuccessfully sought justifies giving some 
attention to the methods and media used when new mem- 
bers of the various genera or species are described. It is 
very easy to obtain great numbers of these mites by drying 
a quantity of galls in open vials ringed inside at the top 
with glycerine to prevent the mites escaping. If these vials 
are then placed in a desicator out of any strong light or heat 
most of the mites will leave the galls in a few hours and 
will be found wandering about the sides of the vials (s. 
Nalepa, 1906 and Hassan, 1928). The question then arises 
how they can be kept permanently and studied at any time 
under the microscope. Various media have been tried and 
found quite useless for anything more than immediate 
study. In all these media (glycerine, glycerine and acetic 
acid, glycerine jelly, balsam, euparal, gum arabic solutions, 
water, alcohol, etc.), the mites are more or less distorted 
and shrunken or become almost transparent, so that in a 
short time the mounts are useless and new specimens are 
needed. Until recently, it was necessary to use alcohol for 
permanent collections and make new mounts from this 
material each time one desired to study the mites in ques- 
tion. The alcoholic material becomes hardened and breaks 
so easily that the specimens are useless for taxonomic work 
a few years after collection. Other media have the same or 
additional drawbacks. Apart from the temporary nature of 
these collections there are the factors of distortion and 
shrinkage to be considered, as well as the improbability of 
being able to re-examine the same specimens at any time. 
Recently, Hassan (1928) developed a method for making 
permanent mounts of the Eriophyidse by modifying a 
