58 FERTILIZATION 



shedding and to fertilize them at once, it seems probable that no 

 increase in O2 uptake would be observed after fertilization. In 

 fact, reference to Fig. 1 1 shows that there might well be a decline 

 in O2 uptake, though at a later stage in embryonic development 

 there would, of course, be the well-known increase in respiration. 

 In nature, sea-urchin eggs are fertilized soon after shedding, for 

 reasons which are gone into at length in chapter 2, Sperm-Egg In- 

 teracting Substances, I. Claims that cytochrome is 'thrown into 

 circulation' at fertilization, or that, before fertilization, there is 

 limited contact between respiratory enzymes such as cytochrome 



■t~i 

 % 

 0^90 



o 





03 



60 



30 





t (hours) 



FIG. 10. — Rate of O2 uptake of eggs of Chaetopterus variopedatm. F, addition of 

 spermatozoa. T° C, 21. The post-fertilization rate is expressed as a 

 percentage of the pre-fertiHzation rate (100), which is —24 /il02/hour/io /tl 

 eggs. After Whitaker (1933a). 



and substrates in the egg (Runnstrom, 1930); or that there is a 

 block in the chain of carriers at this time (Runnstrom, I935«); 

 or that unfertilized eggs are in a biochemically similar condition to 

 insect embryos in diapause (Needham, 1942), lose some of their 

 value in the light of Borei's experiments. It is, of course, interest- 

 ing to know that unfertilized eggs preserve their substrates by a 

 reduction in metabolic activity when allowed to remain unfer- 

 tilized for hours rather than minutes, a frequent concomitant ot 

 their preparation for manometric experiments; but generalisations 

 and interpretations based on a study of biological material in 

 abnormal conditions are apt to be misleading, particularly if the 

 abnormal features have escaped the notice of the experimenter. 



