670 



THE RESPIRATION AND 



[PT, III 



produced by an indicator method, and the oxygen taken in by the 

 Winkler method. In one case the respiratory quotient was 0-78 and 

 in another case 0-72. We are not informed what the age of the embryos 

 was in these experiments, but the second figure was obtained from 

 a batch which was "younger" than the batch which gave the first 

 value. These respiratory quotients are in fair agreement with the 

 fact now definitely known, that there is a very large expenditure of 

 protein in the egg of the plaice to furnish energy during development. 



Kawajiri has studied the embryonic respiration of the Japanese 

 landlocked salmon, Oncorhyncus masou. Apparently the oxygen con- 

 sumption per fish per hour rises steadily until hatching, after which 

 there is a rapid increase, followed by a continued slow rise at much 

 the same slope as before hatching, until the yolk has disappeared, 

 after which time other factors come into play. 



The best work on the respiration of the fish embryo is that of 

 Gray , who in 1926 measured the respiration of the brown trout, 

 Salmofario. His experiments 

 did not begin till the 46th 

 day from fertilisation, about 

 which time the fish escapes 

 from the egg-envelopes and 

 swims freely, existing on the 

 stores in its yolk-sac. The 

 graph given in Fig. 1 26 shows 

 the figures obtained by Gray 

 for metabolic rate. Assuming 

 that the substances com- 

 busted were partly fat and 

 partly protein. Gray calculated that the amount of oxygen con- 

 sumed over the period in question was exactly equivalent to the 

 amount of dry material disappearing from the system. Hayes sub- 

 sequently studied the respiration of the eggs of Salmo salar. It fell from 

 0-075 g'^- oxygen per 1000 eggs per hour on the 40th day to 0-045 on 

 the 65th day. 



In 1928, Boyd, working with the egg of the minnow, Fundulus 

 heteroclitus, and using three methods on the same material (Winkler 

 titration, Fenn's modification of Barcroft's manometer, and the 

 Haldane gas analysis apparatus), found that there was a marked 

 rise in oxygen consumption in the egg after fertilisation. This was an 



10 20. 30 40 50 60 70 80 90100110120130 

 Days from fertilisation 



Fig. 126. 



