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Sect. XT.1 



ZOOLOGY. 



88 J 



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note any traces of vegetable impresiilons In the roclcs, and 

 preseiTe them oarefnlly. 



Seek with the niicrcscoBe for infusorial animals, both in 

 a fossil and recent state. 



On the Use of the Microscope on board Ship. 

 The following remarks embody the experience 



01 



Mr. 



Charles Darwin, F.R.S., on tliis subject, the importance; 

 of which increases as the science of zoology advances. 



TliL- facility in examining the smaller invertebrate ani- 

 mals, either alive or dead, depends mticli more on the form 

 of the microscope used thaa would be at first expected. 

 The chief requisite of a simple microscope for this purpose 

 is strength, firmness, and especially a large stage ; the 

 instruments generally sold in tliis country are much too 

 small and weak. The 



to the upright column and have no movement ; besides 



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the strength thus gained, the stage is always at e 

 the same height, which aids practice in the delicate move- 

 ments of the hand. The stage should be able to receive 

 saucers, three inches in internal diameter. A disc of 

 blackened wood, with a piece of cork inlaid in the centre, 

 made to drop into the same rim which receives the 

 saucers, is usefrd for opaque and dry objects: there should 

 also be a disc of metal of the same size, with a hole and 

 rim in the centre to receive plates of glass, both flat and con- 

 cave, in diameter one inch and a half, for dissecting minute 



lets 



objects ; a plate of glass of three inches diameter 

 in too much light and is otherwise inconvenient. Close 

 under the stage there should be a blackened diaphragm, 

 to slip easily in and out, in order to shut off the ] 



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