654 
.1. DAVIDSON. 
II. Technique and Methods. 
In order to ensure a constant supply of living material, 
several young apple-trees, both in the laboratory orchard 
and in the green-house, were infested with Schizoneura 
lanigera and kept under close obsei’vation. 
For the study of the chitinous exoskeleton, entire specimens 
were treated with cold 10 per cent, potash for several hours, 
and after being washed in distilled water to which a trace of 
acetic acid had been added, were dehydrated, stained in xylol 
saturated with picric acid and mounted in Canada balsam. 
Chloral hydrate and phenol in the the proportion 2 : 1 
proved a useful clearing agent, the insects being left in the 
mixture, which was kept warm until cleared. They were then 
transferred direct to xylol, stained with picric acid or orange 
Gr and mounted in Canada balsam. 
For the study of the head and its endoskeleton the parts 
were dissected out and macerated in cold 10 per cent, potash, 
washed, and examined in glycerine. Glycerine jelly was also 
used as a mounting medium. 
Dissections were carried out on living and preserved 
material under the Zeiss binocular microscope, the specimens 
being fixed down on a small Avax plate beneath the examina- 
tion medium, special parts being isolated and examined on a 
slide. Normal saline solution, glycerine, 70 per cent, alcohol 
and oil of cloves were used as examination media. The 
animals resist wetting very much, which proves troublesome 
Avhen dissecting living specimens under normal saline solu- 
tion. If the surface of the aphid is smeared with 70 per 
cent, alcohol after fixing on the Avax plate, and before pouring 
on the salt solution, the difficulty is overcome. 
Entire specimens Avere fixed with Avarm picro-sulphuric 
acid (Kleiuenberg’’s) foi'mula, and Cariioy’s fluid, the latter 
fixative giving excellent results. Internal organs were 
dissected out in normal saline solution and fixed Avith 
Perenyi’s fluid or corrosive sublimate. 
