PRENATAL GROWTH OF THE PIG 135 



the time of disappearance of the Wolffian bodies^ the kidneys 

 form 1 . 27 per cent of the total weight. Shortly after this, the 

 kidneys increase to 1 . 59 per cent (table 1 ; fig. 2) . 



In the human, the Wolffian bodies form 0.6 per cent of the 

 total volume in an embrj'o of the fifth week (11 mm.), in which 

 the renal anlages are just appearing. From this time onward, 

 they become both absolutely and relatively smaller, just as in the 

 pig, disappearing about the beginning of the third month (31 mm.). 



The Wolffian bodies in the pig are therefore relatively much 

 larger than in the human embryo, and persist for a longer time. 



Differences according to sex 



The data from the various litters were sorted out and grouped 

 according to sex, the averages being calculated for each sex in 

 each litter. Theresults were of little value, however, on account 

 of the small number of specimens, only nine litters having two 

 or more of each sex. Although it was therefore not thought 

 necessary to reproduce this table, certain indications which it 

 showed are worthy of mention. 



In the first place, the total body weight almost constantly aver- 

 ages higher in males than in females of the same litter. It is 

 known that the human males average heavier in weight than the 

 females of the same age in prenatal life and at birth. 



The liver in the pig fetus was found relatively heavier in the 

 female in most cases where a comparison was possible. This is 

 also almost constantly true in the human species. 



The gonads, beginning with the time when the sexes are first 

 distinguishable are found relatively heavier in the male than in 

 the female pig, as already mentioned. This is also in agreement 

 with the human species. 



For other organs, no definite conclusions concerning sexual 

 difierences can be drawn, and even those mentioned rest upon a 

 ver}' uncertain basis. Many more observations are necessarj^ 

 in order to distinguish variations due to sex from accidental 

 variations. 



