ME THODS OF S TUD Y. 213 



scope,' described a very convenient form of disc-holder. A 

 sheet of cardboard is glued on either side of a piece of chamois- 

 leather, and the discs are cut out of this with a sharp punch. One 

 surface should be blackened with Indian ink. The specimens are 

 then fixed to the disc with coaguline. A pin can be thrust through 

 the chamois-leather in any diameter, so that a convenient axis of 

 rotation is easily found, or the axis can be varied at pleasure and 

 the specimen can be turned with precision. 



It is always necessary to mount at least two specimens of any 

 sclerite, so that it may be examined on all sides. 



It is astonishing how very different the form assumed by 

 a sclerite becomes with even a slight rotation of the disc on 

 which it is fixed, so that it is often a work of hours to determine 

 its real shape when it is examined with the compound micro- 

 scope. 



The smaller sclerites may be mounted in Canada balsam, but 

 must not be flattened by pressure. 



I find it best to place the sclerite, or group of sclerites, on a 

 glass slip in a drop of dilute alcohol, and the specimen can then 

 be displayed with needles. This is especially necessary when 

 the minute wing sclerites or the parts of the mouth and other 

 complex organs are required, as otherwise the several sclerites 

 will overlap each other, or assume undesirable positions. When 

 the specimen has been arranged, I remove the alcohol with a 

 small piece of filter-paper, and replace it by a drop of absolute 

 alcohol with a pipette. It is necessary to avoid disturbing the 

 specimen during this process, as it soon becomes hard and 

 brittle, so that it is impossible to move its parts without break- 

 ing them. After carefully irrigating the specimen with absolute 

 alcohol, I replace it with clove oil. 



Should any turbidity occur in the clove oil, I place the 

 specimen in a warm oven, or gently warm it over a spirit-lamp, 

 when the turbidity will rapidly vanish. 



I then drain off the clove oil, place a drop of balsam dis- 

 solved in xylol over the specimen, and set it aside under a glass 

 bell. When the balsam is dry, I add a little more, until the 

 specimen is covered with very thick balsam. I then place a 



