300 W, B. KIRKHAM AND H. S. BURR 



at which stage the egg leaves the ovary, for, if the above changes 

 occurred in one oestrus cycle, ail normal eggs in the above 

 condition would go out of the ovary at ovulation, leaving only 

 Group I eggs in the ovary. This condition was not seen. Hence 

 we were forced to find some other explanation of the facts. 



Figure 5 shows in the form of a table the facts described above. 

 The vertical readings show the groups of eggs. The horizontal 

 readings show the periods into which the oestrus cycle is divided. 

 Period a is the division of the oestrus cycle extending from 

 ovulation to the twenty-first subsequent day and covers a period 

 of time in which there is little change in the personnel of the 

 ovary. Period h covers the succeeding six hours; period c, the 

 next six, and period d, the last six hours remaining before ovula- 

 tion. The above figures are only approximate, as the individual 

 variation is too great to permit of any exact data. 



By studying the figure it will be seen that Group IV disap- 

 pears at period c. At the same time the ovary contains Groups I, 

 II, III and V, IV and VI being absent. During the interval be- 

 tween periods c and d Groups I, II and III remain unchanged, 

 but Group V disappears and Group VI appears. 



After ovulation we find in period a, Groups I, II and III only. 

 But in period h, II disappears and IV appears. 



From the above data we were led to believe that the develop- 

 ment of an egg follows the arrows in the diagram. That is, 

 that Group II comes from I in period c, remains unchanged 

 through d and a, becomes transformed into III during period 

 h, remains unchanged through c, d and a, grows to IV in 6, to 

 V in c and to VI in d, and so out at ovulation. 



The above explanation of the facts rests on the assumption 

 that the normal rate of development is approximately the same 

 for all eggs. This assumption we think is warranted, for if II 

 developed into IV during period h instead of remaining unchanged 

 until the next oestrus cycle, the number of Group III eggs 

 found should be very small, since the change would be a rapid 

 one. On the other hand, if the development involved a longer 

 period of time — that is, if Group III became a second resting 

 stage— one would expect to find a comparatively large number 



