2.3G 



THE USE OF THE MICROSCOPE 



Vi i^ii 



Fig. 2G. — First spermatocyte of grasshopper, Chortophaoa sp. Iron-aceto- 

 carmine preparation. This cell was over 10 microns below the cover, and 

 hence gave a foggy image with an oil-immersion objective of 1.4 aperture. 

 Drawn with a dry fluorite 4.3-millimeter objective of 0.85 aperture with a 15 

 compensating eyepiece, the tube length being increased to 200 millimeters. 

 Objective corrected for a cover-glass 0.18 millimeter thick. Cover-glass, 0.135 

 millimeter. Camera drawing. 



Fig. 27.- — Same cell as in Fig. 26, but turned over and pressed out on the cover- 

 glass. Viewed with apochromatic objective 90 of 1.4 aperture, with a 15 eye- 

 piece. Tube length increased to 173 millimeters. The 11 bivalents and the 

 univalent sex chromosome are shown. Chiasmas are distinguishable at some 

 nodes. Camera drawing. 



