64 FERTILIZATION 



(CO2 produced)/(02 consumed). Such measurements are technic- 

 ally rather difficult to do immediately after fertilization, when sea- 

 urchin eggs are the biological material, for the following reasons: 

 first, the primitive method of measuring R.Q. by having two mano- 

 metric flasks containing eggs and absorbing the evolved CO2 in 

 one of them (which gives — O2), but not absorbing the evolved 

 CO2 in the other flask (which gives +CO2 — O2), does not work; 

 because sea-urchin eggs, unlike those of the oyster (Cleland, 

 1950a), respire at higher rates when the bicarbonate content of the 

 sea water is normal than when it is low, following the absorption 

 of CO2 from the gas phase. Secondly, CO2 retention must be 

 measured. This is troublesome and necessitates the use of mixtures 

 containing known tensions of CO2 in the gas phase. Thirdly, un- 

 fertilized sea-urchin eggs which have been prepared for mano- 

 metric experiments and may, therefore, have been out of their 

 ovaries for more than an hour, have a low rate of metabolism, as 

 can be seen from Figs. 9, 11 and 13, and are easily damaged by 

 being shaken in manometers. These difficulties in the systematic 

 repetition of experiments on unfertilized eggs may drive the ex- 

 perimenter to the dangerous expedient of selecting experiments in 

 which 'everything went well'. The apparent R.Q. of unfertilized 

 sea-urchin eggs is about 1-4 (Laser & Rothschild, 1939); earlier 

 workers, such as Ashbel (1929) and Borei (1933) obtained somewhat 

 lower figures, i-i and 1-1-2. These experiments only tell one that 

 the ratio (CO2 produced)/(02 consumed) is greater than unity in un- 

 fertilized eggs. They provide no information about the nature of the 

 endogenous substrate being metabolized, because the experiments 

 do not enable any distinction to be made between respiratory CO2 

 and CO2 displaced from the sea water by acid diffusing out of the 

 eggs. An overall R.Q. of more than i very probably indicates that, 

 in these circumstances, acid is being produced by the eggs ; but in 

 the absence of information as to how much, we cannot tell what 

 the true R.Q. is, and, therefore, what substrates are being utilised. 

 The delicacy of unfertilized sea-urchin eggs has already been 

 mentioned. The possibility that shaking them in manometers in- 

 duces a pathological formation of acid requires further investiga- 

 tion. 



In rock-oyster eggs, the R.Q. is 0*8 before fertilization, which is 

 interpreted by Cleland (1950^) as being due to the eggs metabolis- 

 ing a mixture of carbohydrates and lipids. The R.Q. is also lower 



