SECT. 4] HEAT-PRODUCTION OF THE EMBRYO 641 



4-3. Rhythms in Respiratory Exchange 



From the researches we have so far been discussing no evidence 

 has been found of a rhythmical activity in the gaseous exchange of 

 echinoderm eggs. Lyon's paper of 1904 has been referred to, how- 

 ever. "In nearly all experiments", he said, "there was an increase 

 in CO2 production during the first ten or fifteen minute interval 

 following fertilisation. The increase was slight, and sometimes could 

 not be detected. Following this came an interval in which the GOg 

 production was small, visibly less indeed in two or three experiments 

 than that of the unfertilised eggs and sperm. This is the mid-period 

 of cleavage, approximating perhaps to the time of nuclear growth and 

 the early stages of karyokinesis. The interval during which the eggs 

 were dividing into the first two blastomeres was one of active GOg 

 production. After this period came an interval of lessened produc- 

 tion. In one or two cases a second rise occurred at about the time 

 of the second cleavage." And in his second paper on respiration 

 and susceptibility, he said, "It may be stated that the apparent 

 conclusion was that GO2 production in the egg is not uniform through- 

 out the whole series of morphological changes in cell-division, but 

 rather reaches a maximum at the time when the cytoplasm is actively 

 dividing. Furthermore it seemed that at the time when oxygen is 

 most necessary and presumably is being used in largest amount (as 

 indicated by susceptibility to lack of oxygen and to KGN) GO2 is 

 produced in largest amount. If the conclusion above expressed 

 should justify itself it would indicate that oxygen is used chiefly 

 in the egg for synthesis rather than for combustion, and that the 

 larger part of the GO2 comes from spHtting processes. One would 

 also infer that the energy for cell-division comes from fermentative 

 rather than oxidative processes". Obviously these points were of 

 great importance for a knowledge of the metaboHsm of the egg 

 during the earliest stages of its development, and it was unfortunate 

 that Lyon gave no figures in support of his opinions. The theories 

 of cell-division subsequently associated with the names of Robertson, 

 McGlendon, Spek and Heidenhain would then have been easier to 

 assess, for they all postulated the existence of some more or less 

 actively contractile mechanism in the cell during cleavage in contra- 

 distinction to the theory of Gray, in which cleavage is essentially 

 due to a rearrangement of the different cell-phases round the growing 



