ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
667 
Model No. III. (fig. 69) does not differ very much from the pre- 
ceding. The stage is provided with cross-divisions for the orientation 
of the preparation ; but if required the mechanical stage of model No. II. 
can also be applied to this instrument. The draw-tube is only movable 
by hand, and carries no millimetre divisions. 
In model No. IV. (fig. 70) the stage is fixed. The only focal adjust- 
ment is by rack and pinion, which, however, is sufficiently fine for the 
