Prenatal Growth of the Human Body. 145 



The spleen averages relatively larger in the female for each month 

 from the 4th onward, excepting the 4th and 9th, in which the male 

 ii^ larger and in the 9th, where data for the female are wanting. 



The kidneys are almost constantly relatively heavier in the male. 

 In the 4th month, however, the kidneys average larger in the female, 

 and also in the full-term still-born (only 1 female). No data are 

 available for the female in the 9th month. 



The suprarenal glands, unlike the kidneys, are usually relatively 

 larger in the female. The only exception is the 6th month, in which 

 the left suprarenal only averaged larger in the male. ISTo data are 

 available for the 9th month, or for the female in the full-term still- 

 born. 



Comparison ivith other Species. 



A comparison of the growth in the human body with that in the 

 lower animals should be of value in enabling us to judge as to which 

 phenomena are common to various animals (and therefore probably 

 more fundamental in significance) and which are peculiar to the 

 human species. 



It is possible at present to make such a comparison only to a very 

 limited extent, owing to the lack of data concerning growth in the 

 lower animals, particularly prenatal growth. 



We m.ay consider first the rate of prenatal growth in the body as 

 a Avhole. It is a matter of common observation that in forms with 

 eggs of the holoblastic type of cleavage there is during the early stages 

 of segmentation a period during which the cells divide actively, with 

 little or no increase in volume. In fishes and amphibia, this initial 

 period is longer than in the higher vertebrates. In the frog embryo, 

 Davenport (10 a) has shown that after hatching the growth rate in- 

 creases up to the 10th day (with coincident increase in the percentage 

 of water), after which it decreases rapidly. Even during the initial 

 period, while the segmenting ovum as a whole remains nearly sta- 

 tionary in size, the actual amount of protoplasm is increasing rapidly 

 at the expense of the yolk material. 



His (21) in 1868 concluded that the relative growth in the chick 

 is greatest at the beginning, a conclusion supported to a certain extent 



