824 



BIOPHYSICAL PHENOMENA 



.Williams) 



permeable to the salt of the environment as the embryo develops. 

 This finding requires confirmation, Remotti has also studied the 

 thermal expansion coefficient of teleostean eggs, which he claims 

 differs slightly from that of sea water. He found that it definitely 

 augmented during development. 



The specific gravity of the amphibian embryo received a careful 

 examination at the hands of Williams, whose data are plotted in Fig. 

 20 1. In all cases, there is a fall 

 during development which is 

 not interrupted at hatching. No 

 doubt this is due to the absorp- 

 tion of water which is going on 

 at that time (shown in Fig. 230). 

 It must be remembered that 

 the frog embryo is not separated 

 from the yolk, so that the water 

 absorption is not necessarily 

 into the embryonic tissues. 

 Williams also studied the centre 

 of gravity in the frog embryo, 

 finding that in the pre-hatching 

 stages it was always at the 

 cephaHc end of the body, but 

 afterwards, as the yolk was disappearing, it moved to the caudal end. 

 Bialascewicz's figures for the specific gravity of frog larvae are in 

 complete correspondence with those of Williams. 



Hardly any investigations have been made of the specific gravity 

 of the constituents of the hen's egg, except the very early one of 

 Baudrimont & Martin de St Ange, who reported in their famous 

 memoir of 1 846 the specific gravity of various samples of yolk. The 

 figures were as follows : 



Table 95. 



mm. length 

 Fig. 201. 



