13& SELECTION AND TTSti 



Where animalcule cages are not accessible, a small animal 

 may be held between a common slide and a thin cover. To 

 prevent crushing it, a hair or even a thread may be placed be- 

 tween the cover and the glass. A German author recommends 

 the use of fine gauze or netting, in the meshes of which an 

 animalcule may be held very conveniently. Acting on this 

 idea, we took a thin metal plate, and bored it full of holes of 

 various sizes. An animalcule placed in one of these holes may 

 be kept in the field of view for any length of time, and exhibited 

 to those who desire to see it, but it cannot be kept quiet for 

 scientific examination. We like a piece of fine wire-gauze, 

 better than cotton or linen netting. 



Growing Slides, Where it is desirable to keep the same 

 living object for a considerable time, so as to watch its changes, 

 it is necessary to use what is called a growing slide, by which it 

 may be regularly supplied with air and moisture. A large rtuni- 



Pig. 37. GROWING SLIDE. 



ber of complicated devices have been described for this pur- 

 pose, but the following simple contrivance answers the end 

 very well; we have used it for years. To one end of a common 

 slide with a concave centre, cement a small bottle, as shown in 

 the figure. This is easily done by means of a little marine 

 glue. The glue, cut in small pieces, should be laid on 

 the slide at the point where the bottle is to be attached; 

 the slide is then to be gradually heated until the glue is 

 softened, when the bottle is laid on and moved back and 

 forth until it has been thoroughly imbedded in the cement. 

 The bottle is filled with water and corked, the upper side 

 of the cork having two notches cut in it, one for the en- 

 trance of air, and the other for the passage of a loose cotton 



