114 A HUMAN EMBRYO BEFORE THE APPEARANCE OF THE MYOTOMES. 



(1907) specimen, the age of which is estimated at (18) 19 days. The embryo 

 Kl. 13 of Grosser ( 1913) is strikingly like our own, but we think a trifle more devel- 

 oped. Grosser gives the age as 19 days. A very similar stage of development is 

 represented by the recent embryo of Strahl (1916), but concerning which there are 

 no data as to age. 



If one again adopt the method of Bryce and Teacher, it is possible to determine 

 when, as regards the menstrual cycle, fertilization took place. The duration of the 

 menstrual cycle in this case may be taken as 25 days regular 24 to 26 and if we 

 let the age of the embryo be 18 days, then fertilization occurred on the seventeenth 

 day of the previous menstrual month. Such a date would harmonize very well 

 with the findings of Frankel on ovulation, as interpreted by Grosser. The time 

 thus assigned for fertilization could easily be pushed still farther toward the begin- 

 ning of the menstrual month by either supposing that the embryo is more than 18 

 days old or that development was arrested by the hemorrhage some time before 

 abortion occurred. As regards the last point, we see no reason to suppose that 

 development stopped very long before the ovum was expelled. Fertilization on the 

 seventeenth day of the menstrual cycle would mean that the intercourse of April 2 

 could not be considered in computing the age, since it falls on the twentieth of the 

 cycle, 15 days prior to. the abortion. 



The history of intercourse two weeks before the one just noted is, however, 

 subject to doubt; it would have occurred on the sixth day of the cycle. This would 

 have called for a rather protracted sojourn of the spermatozoa within the tube- 

 namely, 11 days, a period over which they are doubtless quite capable of retaining 

 their fertilizing power. The sixth day of the cycle would fall about the beginning 

 of the so-called period of oestrus, and, in view of the reputed increase in libido at 

 this time and of certain obstetrical experiences, one may suppose that not only is 

 this a favorable time for insemination, but also favorable to a prolonged stay of the 

 spermatozoa within the tubes. 



The arrival of the ovum in the uterus and the date of its implantation are 

 dependent upon the unknown factor of the time consumed in traversing the tube. 

 Grosser points out that this may vary, depending upon tubal (menstrual) conditions, 

 and he is inclined to raise the estimate of 10 days, given by himself and Triepel, to 

 14 days or even more. In either case, implantation would have occurred after the 

 beginning of the lapsed period, and some influence other than that of the actual 

 ovum upon the uterine mucosa would have to be invoked to inhibit the impending 

 menstruation. Such an influence, as is well known, has been sought in the tiny 

 ovum within the tube, acting alone or in conjunction with the newly formed corpus 

 luteum. Assuming 10 days as the period of migration (7 days in the table of Bryce- 

 Teacher), implantation would have occurred in our specimen on the second day of 

 the cycle. It would therefore have found a mucous membrane especially adapted 

 to its nutritional needs, possibly thus accounting for its large size as compared with 

 the stage of development; but, on the other hand, the inhibitive action upon this 

 same mucosa, from whatever source, may have come too late to save it, as seems also 

 to have been the case with the Bryce-Teacher ovum. 



