TIME RELATIONS OF PARTURITION, MATURATION, ETC. 1 5 



IV. TIME RELATIONS OF PARTURITION, MATURATION, OVULA- 

 TION, INSEMINATION, AND SEMINATION. 



Parturition may occur at any hour of the day or night; although, 

 as table 3 shows, it takes place more frequently in the early morning. 



Table 3. — Number of cases of parturition during each of 6 four-hour periods of a day. 



The distribution is nearly the same whether the periods begin at 

 4 a.m. or at 6 a.m. 



The eggs which mature at each ovulation average nearly seven, and 

 are in general fairly evenly divided between the two ovaries. In the 

 maturation processes of the eggs of each individual there is a synchro- 

 nism which appears tolerably exact when the adopted stages cover fairly 

 long periods; more specifically, in most cases all the eggs of a given mouse 

 are in one or the other of the following stages: with (1) the germinative 

 vesicle, or (2) the first maturation spindle, or (3) the first polar cell and 

 second spindle. It rarely occurs that the eggs from one ovary are very 

 much in advance of those produced by the other; in fact, a marked 

 difference was observed in only two mice, and in these the most widely 

 separated stages exhibited, on the one hand, the germinative vesicle, 

 and on the other, the first polar cell and second spindle. Between eggs 

 from the same ovary there is still less difference. 



If, however, the processes of maturation are divided into shorter 

 periods, as in table 2 (p. 14), the synchronism appears less perfect. 

 Neglecting, for the time, mice with eggs in the stage of the second spindle 

 (VIII, table 2) — a stage which may persist for 24 hours or more — and 

 considering only those (50 in number) which show eggs in stages between 

 the beginning of the formation of the first spindle and the abstriction of 

 the first polar cell, inclusive (Stages II to VI inclusive), it was found 

 that in a few less than half the mice (22) each individual had all its 

 eggs in only one stage (either Stage I, III, IV, or VI), while the other 

 28 mice had eggs which fell within some two or three consecutive stages 

 from Stage I to Stage VII. In no individual were the eggs confined to 

 either of the single Stages II, V, VII. In other words, one or the other 

 of two conditions prevails; either, first, all the eggs from a given mouse 

 may be in one or the other of the four following stages: (I) the ger- 

 minative vesicle, (III) the first spindle with the chromosomes not yet 



