ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



861 



round which is sunk a groove 0*1 mm. deep and 1 mm. broad, into 

 which the cover-glass fits so that its upper surface is flush with that 



Fig. 175. 



of the slide. Such a chamber is the more easily heated, since the 

 glass itseif acts as an insulator to the stage. The hot-wator apparatus 



