228 
Notes . 
many cases this is of no importance, for instance when there is no 
difficulty in finding again the individual which has previously been 
under observation, or when it is not desired to observe constantly the 
same individual, yet it is a very great drawback in other cases. I have 
therefore devised an arrangement which allows of the slide being kept 
constantly on the stage of the microscope and thus of the continuous 
observation of the same individual 1 for weeks and even, under certain 
conditions to be mentioned later, for an indefinite period. Whilst it 
is based on the principle of Pagan’s growing slide/ almost every 
detail is different in my arrangement, and its new features justify its 
publication. I have had it in use for the last six months, and I may 
say that the results which I have obtained in growing Algae were 
extremely satisfactory. 
Fig. 12. Fig. 13. 
The arrangement which is represented on Figs. 12 and 13 requires 
very little explanation. Fig. 12 represents the essential parts of the 
apparatus. The slide, A, has the ordinary form, but is made slightly 
longer than the stage of the microscope, so as to project a little at 
both ends. On it is placed a piece of ordinary blotting paper, B, 
which just leaves the margins of the slide free ; a hole is cut out in the 
centre of this paper, C, and at one end is a triangular prolongation, 
B', which is bent downwards close to the slide. Water is drawn from a 
tumbler, E, by means of a capillary tube, D, and drops on to the blotting 
paper. I usually make the tube just wide enough to allow a small 
drop of water to escape about every 20 seconds. The water is drained 
Of course only as long as it is in a non-mobile state. 
