I050 



CARBOHYDRATE METABOLISM 



[PT. Ill 



From this they concluded that lactic acid was formed normally by 

 the developing sea-urchin's egg, and that if its oxidation was in- 

 hibited it accumulated as in all other cells. There was a hint of more 

 rapid formation after fertilisation. It will be recalled that Meyerhof 

 in 191 1 (see the Section on Respiration) did not succeed in demon- 

 strating any glycogen or free glucose in unfertiHsed Strongylocentrotus 

 eggs, but that Matthews in 1913 (see the Section on Constitution) 

 had found a Hpoid in Arbacia eggs which contained sugar. In 1927 

 by improved methods Blanchard did demonstrate the presence of 

 traces of glycogen in Arbacia eggs, though not the minutest amount 

 of free glucose. Perlzweig & 

 Barron determined to estimate 

 the total carbohydrate in the 

 eggs before fertilisation, and, 

 using much the same technique 

 as in Needham's studies on 

 the frog, they found about 50 

 mgm. of glucose per gram of egg 

 protein. It is probable, there- 

 fore, that the major part of the 

 carbohydrate in Arbacia eggs is 

 present as a mucoid. 



As has already been indicated 

 in the Section on Energetics, re- 

 spiratory quotients closely ap- 

 proaching unity have frequently 

 been obtained during the cleavage stages of echinoderm eggs. Barron 

 has recently been able to fertilise Arbacia, Asterias and Nereis eggs in 

 strictly anaerobic conditions, a finding which suggests carbohydrate 

 metabolism (see p. 758), the cells piling up an oxygen debt. More- 

 over, direct measurements of glycolysis rate have been made by 

 Ashbel on Paracentrotus eggs : revealing an augmentation of N.G.R. 

 on fertilisation. One mgm. of tgg nitrogen produced 0-845 rngm- of 

 carbon dioxide per hour from the glucose mixture before fertilisation 

 and 2-32 afterwards. It would be still more interesting to compare 

 this N.G.R. with that of later stages up to the free-swimming 

 pluteus (cf Section 4-20). 



Fig. 291. 



