644 



THE RESPIRATION AND 



[PT. Ill 



plotting them together. The rate rises clearly from about 2 1 to about 

 33 per cent, during the 375 minutes elapsing between fertilisation and 

 the end of the 8-cell stage. It is obvious from this graph that the 

 fluctuations in the rate of oxygen consumption bear no relation to 

 the periods of cleavage, but must depend on other variable factors. 

 The curves given by Vies are comparable with the curve for oxygen 

 consumption given by Gray in Fig. 1 1 1 , so that there is a contra- 

 diction between the results obtained by the two methods. In such 

 a case, one can only accept the results given by the most direct and 

 accurate method, so that it is necessary to conclude with Gray that 



50 150 250 350 



minutes 



Fig. 112. 



there are no rhythms in metabolic intensity during the cleavage of 

 the echinoderm egg. For the details of the criticism of Vies' technique 

 the original papers must be referred to. It should be observed that 

 Vies' rhythms of carbon dioxide production do not agree with those of 

 Lyon, for in the former case the period of maximum carbon dioxide 

 evolution occurs immediately after division, and in the latter case 

 during it. The rhythms of Lyon correspond rather to the rhythms of 

 susceptibiUty to various agents which the echinoderm egg has been 

 found to undergo during its cleavage stages. These will be discussed in 

 the Section on susceptibihty. Having decided, then, that the oxygen 

 consumption gives a better measure of the metabolism in a case such 

 as that of the sea-urchin's egg, there remains the possibility that the 

 rhythms observed by Vies in carbon dioxide evolution may be real 



