n8 



PRACTICAL MICROSCOPY. 



Amphipleura pellucida, shown in Fig. 112, is a most 

 difficult diatom to resolve ; indeed, it cannot be accom- 

 plished by any dry objective save 

 of the widest aperture, and even 

 then it requires most careful 

 attention to the details of illu- 

 mination. 



Dr. Woodward considers this 

 frustule to be the most useful 

 test for immersion objectives 

 of \ power and higher. The 

 resolution into lines is not so 



FIG. 109. 



FIG. no. 



FIG. in. 



FIG. 112. 



