COLLECTION OF BDELLOID AND OTHER ROTIFERA. 225 



its movements, and this can be effected either by placing in 

 the water a very few fibres of ordinary cotton wool or a few 

 threads of Spirogjrra or similar Algae. When the cover-glass 

 is placed in position the water-film should be intersected by a 

 thin network of fibres and broken up into numerous small en- 

 closures within one of which should be imprisoned the rotifer. 

 When the captive is a Bdelloid, this procedure is unnecessary. 

 For ordinary observation Bdelloida must never be held in any 

 degree, or they wall not display the corona. In the cells which 

 I use they have plenty of room. The water having been sufii- 

 ciently reduced, the cover-glass is put on carefully and the slide 

 placed on the stage of the microscope to make sure that the 

 water-film does not reach the cell- wall. If it does, the cover- 

 glass must be taken off and put on again until all is right. In 

 such cases it is often advantageous to turn the cover-glass partly 

 round before replacing it. When successfully carried through, 

 the operation, which takes so many words to detail, occupies 

 very little time. I have described the procedure as if dealing 

 with a single rotifer, but in practice I generally pick out several 

 examples and place all in one cell before removing the surplus 

 water. I have had as many as seven different Bdelloid species 

 living happily together for weeks in the same cell, having been 

 introduced one by one in the way described. 



With my cells I use 1-inch square cover-glasses, that size 

 being much more easy to manage when the cover has to be 

 temporarily taken off. 



Many Bdelloida are much scared when transferred to a cell, 

 and either remain obstinately contracted or march about rest- 

 lessly and vigorously. As many species cannot be identified 

 with certainty unless seen when feeding quietly and well placed, 

 I find it best to leave such animals undisturbed in the cell for 

 examination on another evening. 



I have not attempted to keep any Rhizotan species in these 

 small cells, and I find that very few of the free-swimming Ploima 

 will survive in such restricted quarters for more than a few 

 hours. When examination of these animals is finished, it is 

 best to restore them to the original gathering. Such exception- 

 ally hardy forms as Diaschiza gracilis, Metopidia lepadella, 



