ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
335 
which several modifications have been made since it was first introduced. 
The special point of the present form is that it is independent of the 
mirror; it can also he swung to one side and other accessories attached. 
Fig. 24. 
Fig. 25. 
The whole apparatus swings about the axis D (figs. 24 and 25), as 
shown by the outline drawings to the light, and I it has a vertical motion 
