Prenatal Growth of the Human Body. 



123 



according to observations by Waldeyer (44) and Daffner (10). This 

 gives the enormous figure of 574,999 for the relative growth during 

 the 1st month, corresponding to an increase of over 57 million per 

 cent. This number is undoubtedly too high, however, since the fluids 

 enclosed in the membranes and making up a considerable proportion 

 of the total weight, can hardly be fairly considered as products of em- 

 bryonic growth, in the ordinary sense of the term. The true relative 

 growth for the 1st month therefore lies somewhere between 1 million 

 and 50 million per cent. 



From the foregoing, it appears that the relative growth of the 

 human embryo is enormous in the 1st month, declining thereafter, at 

 first very rapidly, then more and more slowly. The next question 



which naturally arises concerns the growth within the 1st month. 

 Some light is thrown upon this question by the observations on the 

 volumes of the His models, recorded in Table II. 



First it may be noted that the yolk sac is relatively large in the 

 early embryos. In the 2 mm. embryo, it makes up more than three- 

 fourths of the total volume. In the 2.6 mm. embryo, the yolk sac 

 remains at about the same absolute size, but owing to the increase in 

 the size of the embryo proper,, it here forms less than two-thirds of 

 the total volume. In my 6 mm. specimen (]!^o. 176) the volume of 

 the yolk sac was .0056 cc., forming a little more than one-third of 

 the total volume, the embryo proper measuring .0098 cc. According 

 to Mall (29) the diameter of the yolk sac is approximately 1 mm. at 

 the age of 1 week, increasing 1 mm. each week up to the 6th. It 

 is therefore evident that although the growth of the yolk sac has 



