224 DAVID BRYCE ON THE 



means of the pipette from the various gatherings or washings 

 examined in the stage trough. When picking up the rotifer it 

 is desirable to take with it as little water as possible. This can 

 be attained to some extent (1) by the use of a very fine pipette 

 of the form shown in fig. 1, e ; (2) by not filling the stage trough 

 more than 1 inch deep. Having captured the rotifer wanted, 

 I gently blow out the contents of the pipette upon a specially 

 prepared cell-slide (fig. 1, d), depositing the water near the centre 

 of the cell. It is essential that when the cover-glass is placed 

 in position, the film of water should not much exceed J inch 

 in diameter, and that it should not at any point reach the cell- 

 wall, the effect of these conditions being not only to provide in 

 the cell a supply of air, but also to very considerably retard 

 evaporation of the fluid contents. In most cases the water 

 taken up by the pipette and deposited in the cell exceeds the 

 desired modicum, and some must be withdrawn. The use of 

 blotting paper for this purpose I find to be slow and risky. The 

 first step is to remove with a forceps to another cell any coarse 

 sand or large fragments of plant or moss. This done, I generally 

 draw up the surplus water into the pipette by capillary attrac- 

 tion only, ensuring that the inflow is very slow by keeping my 

 finger lightly pressed on the upper orifice. The water removed 

 is deposited in another cell, in case, by misadventure, the rotifer 

 may have been caught up as well. If the captured animal is a 

 Bdelloid, it has probably contracted itself when first picked 

 out, and it is well to wait a few minutes before removing the 

 surplus fluid, to give it time to re-extend and regain its foot- 

 hold. But even with all possible care, the animal will some- 

 times get stranded in the pipette. Therefore, when the capture 

 is of more than ordinary importance, I adopt a slower but safer 

 method. Placing the cell-slide flat ujion my table, I take an- 

 other similar slide, and lower it in a horizontal position, face 

 downwards, over the flrst until it rather more than touches the 

 drop of water. It is then carefully raised and brings with it a 

 small portion of the fluid, and this is examined under the micro- 

 scope to make sure that the rotifer has not been picked up. The 

 procedure is repeated until the water is sufficiently reduced. If 

 the rotifer be a " free-'swimmer," it may be desirable to restrict 



