MATERIAL AND METHODS. 13 



potassium permanganate for 10 minutes; rinsed in water; transferred 

 to a 5 per cent solution of oxalic acid for 20 minutes; washed thoroughly 

 in water; and left in the stain for from 18 to 36 hours. The process was 

 completed by a final rinsing, rapid dehydration, and mounting in balsam. 

 The results given in the following pages are based on 1,000 eggs 

 obtained from 147 mice. Only clearly normal eggs have been used, 

 those in the ovaries being in all cases in large ripe or nearly ripe fol- 

 licles, never in small or manifestly degenerating ones. Each egg was 

 carefully studied with a Zeiss 2 mm., homogeneous immersion, apo- 

 chromatic objective and a No. 12 compensating ocular. Sketches and 

 measurements were made for each egg on separate sheets of paper of 

 uniform size (see page 7), which could be subsequently arranged as 

 desired. Tables 2 and 3, which will be referred to again, show in a 

 comparative way the number of eggs in various stages, and also other 

 data to be discussed later. 



