ZOOLOGY AND BOTANY, MICKOSCOPYj ETC. 117 



angle to each other. In order that they may be brought quite close 

 together, those on the arm 1 are fixed perpendicularly to the plane 

 of the disk, while those on 2 are inclined outward, so that the same 

 division can be observed through two Microscopes. 



The illumination of the circle is effected through four tubes / 



Fig. 12. 



attached to the Microscopes, through which by means of concave 

 mirrors and reflecting prisms, the light from four lamps is conducted 

 down on the part of the circle to be examined. 



Prof. W. A. Eogers, it will be remembered, uses for the same 

 purpose the arrangement devised by Mr. ToUes, in which a prism is 

 inserted between the lenses of the objective.* This would appear 

 to be more convenient on the whole. 



* Of. this Journal, iii. (1880) p. 754. 



