180 PROCEEDINGS OF SUCIETIES. 
At 90° to 100°, if the slide be kept free from dust, numbers of 
the most perfect spiral crystals, some right- some left-handed, will 
be seen to cover the slide. (Fig. 5.) 
I have no doubt that some of these crystals are, in reality, cones 
standing out in relief from the slide. Of this I have satisfied myself 
by allowing them to form in a partial vacuum in the receiver of 
an air-pump, and then suddenly letting in the air upon them, when 
I have seen the apex of the cone broken or forced in by the atmo- 
spheric pressure. I may also add that, under all circumstances, 
the erystals thus formed in a vacuum are more perfect than when 
exposed to the air, owing to the exclusion of foreign matters, such 
as small particles of dust, which are apt to interfere with the 
formation of the curves. 
Very beautiful effects may likewise be produced by allowing 
the film to crystallize gradually in Canada balsam. The balsam 
should be gently warmed, but not sufficiently heated to drive off 
the few atoms of water contained in it. The salt gradually ab- 
sorbs this water, and crystallization is slowly effected. 
Dustin MicroscoricaLn Civus. 
November 16th, 1865. 
Dr. E. Perceval Wright exhibited some spirally twisted cases 
of a phryganidous insect, collected by Professor Harvey some 
years ago in Australia. They had been taken, with a large 
