SECT. 6] OF THE EMBRYO 911 



prominent would thus be expected to be more sensitive to temperature 

 change than one in which it is not prominent. As it is difficuh to 

 see why an apparently physical process should be so much affected 

 by temperature, we must suppose that the absorption of water is 

 regulated by chemical means. Galloway observed a regulatory process 

 at work, in that individuals which were placed at 13° for a week, 

 and then changed to a warmer environment, showed a greater in- 

 crease of water than those which had been in the warmer environ- 

 ment from the beginning. 



Table 107. 



Time in days required to attain 

 95 % water 



Highest Medium Lowest 

 temp. temp. temp. 



Rana ...... 2 5-7 20 5 28 50 



Amblystoma ... g 12 27 21 50 70 



Bufo _5^5 7^5 --_ 24 32 ^ 



Averages ... 5-5 8-4 23-5 13-3 36-6 60 



Retardation in \ 

 days, reckoned 



from time re- V — 2-9 18 — 23-3 46-6 



quired at highest 

 temperature j 

 Retardation simi-"! 

 larly calculated ^ — 53 327 — 175 350 



in % ] 



The work of McClure provides an interesting commentary on the 

 great absorption of water by the developing amphibian egg. He 

 found that in the early cleavage and medullary groove stages of 

 Bufo and Rana no cell will store trypan blue. But about the time 

 of hatching (9 days from fertilisation) a change takes place and 

 storage of the dye goes on vigorously, as it is taken up from the solu- 

 tion surrounding the eggs. This is probably because the lymph vessels 

 are formed about the 5th or 6th day from fertilisation and can take 

 the dye granules with the incoming water from the periphery to the 

 interior of the organism. 



6-8. The Chemical Constitution of the Embryonic Body in 

 Birds and Mammals 

 We may now return to the chick embryo. We have to con- 

 sider under the heading of general metabolism a variety of data, 

 among which the percentage constitution of the embryo at different 

 stages of its development is among the most important. This leads 



