418 



A HUMAN EMBRYO OF THE PRESOMITE PERIOD. 



embryo. Whereas the clinical data for any individual specimen may be incom- 

 plete, when used conjointly with data from similar specimens it may prove of 

 decisive value. In the case of two specimens of the same developmental period, if 

 we know, for instance, that one can not be younger than 15 days and the other 

 not older than 18 days, we have then established the probable age-limits for all the 

 specimens of that group. It may be explained here that by the term age is meant 

 the fertilization age; that is, the time elapsing from the fertilization of the ovum 

 to the cessation of development. This term was introduced by Mall (1918), who 

 distinguishes it from the copulation age, which he shows to be approximately 24 

 hours longer. 



Decisive age-data of the character referred to are available in connection with 

 the six specimens listed in chart 2, and we are thus enabled to place limits within 

 which the age of the specimens belonging to our three main groups must fall. In 



Days previous la 

 termination of pregnancy 



4 Bryce-Teacher 



eranched 



U E 



i 



m 



Fetzer 



l 



\ 



Merttens 

 Reichert 



Frassi 

 Eternod 



CHART 2. The possible duration of pregnancy in 6 cases having crucial clinical data. Allowing 24 hours each for the inter- 

 ruption of the menstrual period and the completion of the abortion, the Bryce-Teacher specimen could not have 

 been older than 11 days. The Fetzer specimen is probably not younger than 12 days, and the Merttens specimen 

 not older than 15 days; being in the same stage of development, these two furnish the range of possible age for all 

 specimens of similar development. In like manner the Frassi and Eternod specimens furnish the range of possible 

 age for group 3 i. e., 15 to 19 days. 



the Bryce-Teacher specimen the patient missed her period 10 days prior to the 

 onset of the abortion. If we allow an additional day as the minimum time necessary 

 for the interruption of the expected period, the total minimum age would be 11 

 days. In the Fetzer specimen the last coitus, according to information given by 

 the patient, was at least 6 days before entering the hospital, and 13 days before the 

 removal of the specimen by Curettage. If 24 hours are allowed for fertilization to 

 take place the result is a minimum age of 12 days. In the Merttens specimen the 

 last menstrual period began 21 days prior to the curettement and lasted 5 days. 

 Allowing one day for fertilization, there are left 15 days as the maximum age. 

 Since the Merttens and Fetzer specimens are of about the same stage of develop- 

 ment we are justified in concluding that they can not be older than 15 days or 

 younger than 12 days, as indicated in chart 2. The Bryce-Teacher specimen, being 



