A HUNDRED MICROSCOPICAL OBJECTS 



237 



day or two, press out selected cells. Examine with a water- 

 or oil-immersion objective, using Wratten yellow-green 

 screens . Also try smears fixed in chrom-acetic formalin, and 

 stained with a suitable nuclear stain. Also try Apotettix, 

 which has a quite different diaphase and metaphase. (Wen- 

 rich, Janssens, Harman.) (See Figs. 26, 27, and 28.) 



Fig. 28. — Another first spermatocyte from the same slide of Chortophaga 

 as in Figs. 26 and 27. Viewed with a Leitz achromatic 1.8 millimeter objective, 

 compensating eyepiece 10, and Wratten yellow-green screen. No. 58. Without 

 the screen, the definition is not so sharp. Tube length 180 millimeters. Camera 

 drawing. 



62. Unequal Homologues. — Examine, as in 61, Ortho- 

 ptera with unequal homologues in one or more pairs, or 

 with constrictions in a pair of homologues in different posi- 

 tions (as in Circotettix). Observe these at diaphase; and 

 note that the separation of the pachytene thread into loops, 

 at the internodes at which these inequalities of length or 

 differences of position occur, is between homologues, not 

 between sister strands. (Robertson, Wenrich, Carothers.) 



63. Chromosomes of Mus. — Put small pieces of the living 

 seminiferous tubules (about 1 millimeter across) into a small 

 tube of iron-acetocarmine. After a day or two, press them 

 out under a large cover-glass. Examine with water- 

 immersion objective of 1.25 aperture. Also fix smears 



