ANIMALCULE CAGE. 



91 



instrument in which an object may be submitted to gra- 

 duated pressure between two plates of glass, the parallelism 



Fig. 57. Farley's Animalcule-cage. 



of which is perfectly maintained. The class of investiga- 

 tions in which the compressorium is valuable, is that in 

 which such structures as the minute ovum need be closely 

 scrutinised, without any further change in their shape 

 than may render their contents more distinctly visible. 

 For such purposes, a steady hand and a well-made animal- 

 cule cage, such as the one previously described, will answer 

 very well. 



Smith and Beck's troughs for chara and polypes, a sec- 

 tional view of which is shown at fig. 58, are made of three 

 pieces of glass, the bottom being a thick strip, 

 and the front a of thinner glass than the back 

 b ; the whole is cemented together with Jeffery's 

 marine-glue. The method adopted for confining 

 objects near to the front glass varies according b 

 to circumstances. One of the most convenient 

 plans is to place in the trough a piece of glass 

 that will stand across it diagonally, as at c ; then 

 if the object be heavier than water, it will sink, 

 until stopped by this plate of glass. At other 

 times, when used to view chara, the diagonal 

 plate may be made to press it close to the front 

 by means of thin strips of glass, a wedge of glass 

 or cork, or even a folded spring. When using 

 the trough, it is necessary that the microscope Fig - 58 - 

 should be in a position nearly horizontal. 



Dissecting Knives, &c. Knives and needles of various 



