THE RHYTHM OF GOXADAL FUNCTION 587 



ever, may be regarded as minor. It is interesting, furthermore, that the 

 work of all of these investigators (Fraenkel, Huge, Meyer, etc.) indicates 

 the occurrence of fresh corpora and consequently of ovulation at any 

 postmenstrual time up to the close of the third week. 



During the war, German gynecologists (Siegel, Pry 11, Jaeger, Nurn- 

 berger, Zangmeister) recognized the unusual opportunity to study the in- 

 cidence and length of pregnancies which could be dated from a single 

 copulation in these instances pregnancies resulting from cohabitation 

 during very short military furloughs of the husbands. These studies 

 have shown that the majority of such conceptions occur in the first portion 

 of the cycle, Siegel claiming that fifty-two per cent of them occur 

 in the interval from the sixth to the twelfth day. 14 This corresponds nicely 

 with the average time of ovulation according to the histological researches 

 of Meyer and Huge and would tend to show that in man, as in other 

 mammalia, the time of fruitful cohabitation coincides with that of ovula- 

 tion, showing a short life-span of the free ripe male or female sex elements. 

 Here again, however, it must be admitted that the conception data show 

 clearly that pregnancy may follow coitus at any time in the cycle, for 

 example, even on the very last day of the cycle, the expected menses being 

 prevented. 



The third method of determination of the time of ovulation consists 

 in comparing the exact development of very young human embryos of 

 known copulation age. In the mammalia, embryos of the same copulation 

 age show a remarkable uniformity in development so that we would be 

 obliged from this alone to assume a rather constant time for ovulation, 

 fertilization, tubal journey and implantation as well as development even 

 if all these phenomena were not independently determinate by anatomical 

 study. Triepel, Grosser and Mall have argued with great force that we 

 should be slow to postulate a radical difference for man. If the time of 

 ovulation varied as widely as some of the foregoing statistics would seem to 

 demand, then this alone is probably the greatest variant in the whole series 

 of processes in early embryonic stages. If marked variations were found 

 in the degree of development of embryos of the same copulation age then 

 it would be logical to postulate variation in ovulation, fertilization, tubal 

 journey or the speed of development. If such variation does not appear, 

 then we can justifiably look upon the ovulation time (which probably con- 

 ditions fertilization) as constant. Furthermore, if embryos of the same 

 copulation age show essentially similar development, regardless of the 

 particular time of occurrence of coitus in the menstrual cycle, the facts 

 could hardly be explained by the assumption that the time of ovulation in 

 such pregnancies occupies a constant relation to the menstrual cycle, but 



** But see here Pryll, Jaeger, Nurnberger and Ruge, the last of whom has collected 

 all the cases previously reported and reports 24 per cent of such conceptions occurring 

 from the first to the ninth day and 26 per cent from the tenth to fourteenth day. 



