Microscopical Society of Victoria 
67 
being transferred to its appropriate slide till a sufficient number 
have been secured, but if the forms are more numerous it will be 
advisable to collect only four or live species at once, going over 
the material a second time for the remainder. When as many 
diatoms are obtained as may be thought requisite, the slide is to 
be cleaned from the debris of broken valves, etc., which will 
generally have accumulated round the group of diatoms, and this 
may be best accomplished by removing the extraneous matter 
to a safe distance with the needle, and then wiping it 
off the slide with a soft piece of cork, which, if it be cut with a 
clean edge, may be passed very close to the group without disturb¬ 
ing it. The covering-glass may now be applied, but unless the 
diatoms be qidte flat, it should not rest directly upon them, but 
should be supported under one or both edges by fine hairs, single 
fibres of silk being thick enough in many cases. If this precaution 
be neglected, the running-in of the balsam will draw the cover 
down closely to the slide, and, if the diatoms are very convex, or 
have broad hoops, they will be crushed. With species of 
Campylodiscus , etc., I have found it necessary to use supports 
of card, as even stout hairs were not thick enough to protect the 
diatoms from pressure, but it is rarely that anything more is required 
than a single hair under one edge of the cover. A small drop of 
soft balsam is next to be placed on the slide at each of two 
opposite points of the cover, and the slide is to be warmed just 
enough to cause the balsam to run in with an almost imperceptible 
motion, the two waves meeting as near the group of diatoms as 
possible. This is the most critical point in the whole operation, 
since if the slide be warmed too much, causing the waves of balsam 
to run in too rapidly, or if the waves do not meet at the proper 
point, the diatoms will be very liable to be scattered. After the 
balsam has run in and filled the space beneath the cover, it only 
remains to clean off the superfluous balsam, and finish the slide. 
With the utmost caution it is difficult to mount some diatoms 
satisfactorily in the above manner, and in no case is this difficulty 
so marked as in mounting specimens of Campylodiscm, for, though 
of large size, their peculiar shape precludes their having any firm 
hold of the slide, and the balsam is certain to disperse them. 
After various futile expedients to overcome this obstacle in 
