PRENATAL GROWTH OF THE PIG 133 



0.24 per cent. In the adult, they form 0.01 per cent (Vierordt). 

 The suprarenals, therefore, have a much larger relative size in 

 the human than in the pig, both in prenatal and postnatal life. 



Gonads. {Table 1: fig. 4)- The gonads were first accessible 

 by dissection at 25 mm., when they average 0. 13 per cent of the 

 total weight (sex not determined). From this point on, there is 

 considerable difference in the two sexes, the testes (including 

 epididymis) averaging heavier relatively than the ovaries. 

 Rising rapidly to a maximum, the testes form 0.24 per cent at 

 42 mm., decreasing to 0.038 per cent at 242 mm. At 58 mm. 

 the ovaries have their maximum size of . 094 per cent of the total, 

 decreasing to . 014 per cent at 242 mm. At 26 cm. the ovaries 

 (average of two observations) form . 035 per cent of the total 

 body weight. This is probably either erroneous, or an abnor- 

 mal condition, hence the curve in fig. 4 was not extended to this 

 point. In the adult (2 F.) the ovaries form 0.015 per cent of 

 the total body weight. (No data for males). 



A similar relation is also found in the human, the gonads being 

 relatively larger in the earlier part of the prenatal growth and the 

 testes being relatively heavier than the ovaries . In a human embryo 

 of the fifth week (11 mm.), the anlages for the gonads (sex unde- 

 termined) form 0.085 per cent of the total body volume. In 

 the later fetal stages, the human testes are about twice as large 

 relatively as the ovaries, a relation similar to that in the pig. 



Kidneys and Wolffian bodies. The kidneys (table 1 ; fig. 2) 

 were first measured at the 25 mm. stage, where they average . 22 

 per cent of the total body weight. They increase rapidly to a 

 maximum relative size of 2.59 per cent of the total weight at 

 58 mm. At 191 mm. they form . 92 per cent, which is the mini- 

 mum for later fetal life. Near full term they form 1 . 01 per cent 

 of the total, and in the adult, . 24 per cent. There is apparently 

 no constant difference in size between the right and left. 



In the human, the kidneys form about 1 per cent in the later 

 fetal stages. Vierordt gives 0.46 per cent as the relative size in 

 the adult. The human kidneys first appear in the second month, 

 and from that time onward the left kidney is quite usually slightly 

 larger than the right. 



