232 THE AMERICAN MONTHLY [Aug 
. Mr. Burbidge’s failure is fully explained by his having 
killed the rotifers too quickly. They require narcotising 
first and then killing at the right moment. This is Mr. 
Rousselet’s method, as fully explained in the ‘Journal 
of the Quekett Club” for 1893, p. 205. I understand 
that this method has not been tried on polyzoa, but I 
think it 1s worth trying.—J. S. Pratt. i, 
I have tried osmic acid with the fresh-water hydra, 
but only about one in a dozen is passable.—J. Phillips. | 
I have mounted hydrozoa with fully expanded tenta- 
cles quite successfully by the following method: Place 
them in a rather shallow vessel of sea-water and add, 
very gently, a few drops of chloroform-water by means 
of a pipette. At first the hydra will draw in their ten- 
tacles, but if too much has not been given they will ex- 
pand them again. Then add a little more chloroform- 
water. After a while, under the influence of the anaes- 
thetic, the animals will become apparently stupefied and 
cease to draw in their tentacles. Now is the time to kill 
them, and this is done by suddenly pouring over them a 
hot saturated solution of corrosive sublimate. This 
method does also for rotifers. They should be mounted, 
not in glycerine, but in balsam or weak corrosive subli- 
mate solution.—A. Montague. 
I once spent some time trying to mount rotifers, but 
with very little success. It is useless trying to fix them 
instantly with osmic acid. They require to be previously 
narcotised. The difficulty is to know when they are 
sufficiently narcotised for the application: of the fixing 
agent.—J. R. L. Dixon. 
PATTERNS IN GLYCERINE-JELLY Mounts.—Many years 
ago I was much troubled with the beautiful patterns 
produced by the vaporization of glycerine jelly. After 
spoiling a number of slides 1 decided to do no more 
glycerine-jelly mounts, but to keep to balsam. An ear- 
