ARTHROPODA 175 



for any reason, it is desired to hasten the process, the specimens 

 should be placed in a thermostat at a temperature of 40 or 50 and 

 allowed to remain there for half a day or one day. For boiling, a 

 water-bath should be used, into which the glasses containing speci- 

 mens and solution are plunged. In the case of the larger varieties 

 the process will take several hours. 



As a general rule, the objects are sufficiently macerated when they 

 begin to acquire transparency. The remains of the solution, together 

 with the softer body-parts, which will now have become soluble in 

 water, are rinsed out with distilled water, to which a drop of glacial 

 acetic acid has been added. The solution is poured off and replaced 

 by the acidulated water, which is changed repeatedly until the 

 objects become light and clear, the process being watched under the 

 microscope. The objects are now taken out of the water and laid 

 upon a glass slide, some with the dorsal, others with the ventral, 

 surface uppermost. If there is only one specimen, it should be first 

 viewed from the ventral aspect. The object should be arranged, with 

 the aid of the microscope or strong magnifying glass, with a fine 

 brush ; the extremities should be extended, and the water removed 

 with filter paper. Props of suitable thickness should be conveniently 

 placed and the specimen covered with a cover-glass. Weak alcohol 

 should now be very carefully added and replaced, after a short interval, 

 by stronger alcohol. If the objects are to be mounted in balsam, the 

 cover-glass should be removed as soon as they have become hard ; 

 they should be dehydrated with strong alcohol, cleared with oil of 

 cloves, and then mounted. Delicate objects become too clear when 

 mounted in balsam, and these should be put through the alcohol and 

 glycerine stages to pure glycerine ; or the chitinous substance may be 

 coloured with carmine or aniline stains ; or Mayer's mixture (a solu- 

 tion of pyrogallic acid in alcohol or glycerine) may be used. Super- 

 fluous colour is removed with a weak acid solution, and the specimens 

 should be mounted in balsam, glycerine, or glycerine-gelatine. 



Maceration in potassium solution may be omitted in the case of 

 small, transparent, slightly coloured parasites, but only when these 

 are obtained alive. They should be put on to a glass slide, covered 

 with a cover-glass, and, as soon as their legs are extended, killed with 

 alcohol, 1 which should be introduced under the edge of the cover- 

 glass. They are then finished and mounted in either glycerine or 

 balsam. On account of the impermeability of the chitinous envelope, 

 specimens which are to be mounted in balsam must be carefully 



1 The legs of the larger varieties of Acarina will usually become extended if the 

 parasites are killed in boiling water. For the smaller varieties a mixture consisting 

 of 2'5 glycerine, 4'0 glacial acetic acid, and 93'5 alcohol, should be employed. 



