TIME RELATIONS OF PARTURITION, MATURATION, ETC. 19 



assume that the first part of maturation in a large majority of cases 

 occurs between the 14-hour and the 18-hour epochs p.p. While it is 

 quite possible that the first part of maturation requires fully 4 hours 

 (as for example from 14 to 18 hours p.p.), it seems highly probable that 

 it may be accomplished within 2 hours, for the reason that at the 

 16-hour epoch as many eggs have reached the second part of matura- 

 tion as are still in the first part. If that assumption is true, the process 

 beginning at 14 hours p.p. would be finished at 16 hours, that starting at 

 16 hours would end at 18 hours, and so on. 



The second part of the maturation process the formation of the 

 second spindle, the division of the spindle, and the formation of the 

 second polar cell probably requires only a very short time (perhaps 

 only a few minutes). But the period when this takes place depends, 

 as Tafani and Sobotta have pointed out, on the time of semination, 

 this part of the maturation process being apparently dependent on the 

 stimulation due to the presence of the spermatozoon in the egg. 



Now, the earliest stage of an egg containing a spermatozoon that 

 we have observed came from a mouse killed 20^ hours p.p., but most of 

 the fertilized eggs were obtained from animals killed between 23 and 

 31 hours p.p. Thus generally the second part of the process occurs at a 

 period which begins somewhere between 2\ (20^ minus 18) and 17 (31 

 minus 14) hours after the completion of the first. Consequently the whole 

 process of maturation probably requires not less than 4 hours. However, 

 as we have seen (p. 1 7) , the first part of maturation may occur quite late 

 as late as 28^ hours p.p. In such case it is entirely conceivable that 

 spermatozoa might reach the oviduct simultaneously with the eggs, and, 

 as a result, the second part of maturation might not be delayed but begin 

 immediately on the completion of the first. 



It must be concluded, then, that the process of maturation (i.e., 

 from the disappearance of the germinative vesicle to the completion of 

 the second polar cell) may be accomplished within about 2 hours, but 

 probably requires more, from 4 to 15 hours, the longer period (above 

 4 hours) being due to delay in the time of semination. 



The time of ovulation is not rigidly fixed with regard either to par- 

 turition or to the maturation of the egg. Table 2 shows the location 

 (ovary, oviduct, etc.) of eggs in the several stages, and table 4 the in- 

 tervals p.p. when eggs in Stages III.IV6, VI, VII, and VIII were obtained. 

 Also, table 4 does not include all the mice whose eggs fall in the above 

 stages, but only those bearing on ovulation. Two mice (Stage IV b, 

 table 2 and table 4), one killed 14! and the other 18^ hours p.p., showed 

 in the periovarial space two eggs and one egg respectively. Each of the 

 three eggs had the first spindle in the "equatorial-plate" stage with 

 circumpolar bodies. The ovaries contained other eggs of the same 

 stage in ripe follicles. Referring again to tables 2 and 4, the eggs in Stage 

 VI were all found in the ovary except four (from two mice killed i6| and 



