124 C. M. Jackson. 



been relatively very great during the first two weeks, its later growth 

 is much less rapid. 



As to the embryo proper, the actual volume at the end of the 2d 

 week (2.2 nun.) is seen to be .000781 cc. As tlie volume of the 

 ovum at the beginning is about .000004 cc, this corresponds to an 

 increase of 195 times in volume during the first half of the 1st month. 

 During the second half of the 1st month, the embryo proper increases 

 from .000781 to about .04 cc, or about 50 times. It is therefore 

 evident that the growth of the human embryo is relatively more rapid 

 during the first half of the first month than during the second half. 

 The difference would appear still greater, if the growth of the yolk 

 sac, membranes, etc., was taken into account.^ 



From what we know of the development in lower animals, as 

 Donaldson (11) has pointed out, there is probably no increase in 

 volume during the early segmentation stages of the ovum ; so that the 

 increase must be all the more rapid when it actually begins. 



In addition to the observations in Tables I and II, a considerable 

 amount of data concerning the prenatal growth of the whole body 

 from the 4th to the 10th months has already been published. Ahl- 

 feld (1), Fehling (16), Legou (25), Faucon (15), Michaelis (35) 

 and others have recorded the weight of fetuses whose age was es- 

 timated from menstrual histories. Curves of absolute growth for 

 the prenatal period, based upon these data, are sho\^rti in Fig. 1, 

 (curves 1, 2, 4, 5). ]^o curves are sjiown for the data of Faucon 

 and others which do not differ materially from those given. From 

 all the data available, I have ventured to construct a normal curve 

 (Fig. 1, curve 3), which is intended to represent the absolute pre- 

 natal growth, according to our present knowledge. As will be seen, 

 it does not differ greatly from that based upon the data of Fehling 

 (who utilizes also observations from Hecker and Schroeder). Ahl- 

 feld's figures seem entirely too high for the average weight at the 



^Daffner (10) gives the weight of a fresh "ovum" of fourteen days as 

 0.82 g., which is more than 200,000 times the weight of the ovum at the 

 beginning. During the second half of the third month, however (accept- 

 ing Waldeyer's observations of the 2.3 g. for the weight at the end of the 

 first month), the embryo phis membranes, etc., increases only about three 

 times in weight. 



