6o 



FERTILIZATION 



Borei's findings are of sufficient importance to warrant their being 

 repeated and it is to be hoped that this will soon be done. 



We must now enquire into the reasons for the different respira- 

 tory responses of eggs to fertilization. Three explanations have 

 been put forward, involving respectively the state of maturation 

 of the egg at fertilization, the pre-fertilization level of Oo uptake, 

 and changes in the nature of unfertilized egg metabolism, accord- 

 ing to their and their parents' history. Reference was made in 

 chapter i to the four different states of egg maturation at which 

 fertilization occurs. Table 1 1 gives some details of the ratio (O2 



FIG. 12. — O2 uptake of unfertilized eggs of Arbacia puiirtiilota under sterile and 

 non-sterile conditions. The figures against each curve refer to the number 

 of bacteria per ml. of egg suspension. After Tyler ct al. (1938). 



uptake, fertilized eggs)/(02 uptake, unfertilized eggs) in each of the 

 four classes. Further information will be found in papers by Ballen- 

 tine (1940) and Cleland (1950a). The ratio will be seen to be about 

 I, or less, in Classes 2 and 3, not in general much more than i in 

 Class I, and markedly more than i only in Class 4. There are a 

 few exceptions ; but the different temperatures at which the experi- 

 ments were done and the variations in time after removal from the 

 ovary, may be responsible for these. The table shows, however, 

 that when the nucleus is in what is sometimes called the 'kinetic' 

 state, there is no increase in O2 uptake at fertilization, but that 

 when it is quiescent, Oo uptake increases at fertilization. The in- 

 crease may, in fact, be caused by sperm penetration or the onset 

 of meiosis. The Class 2 situation, in which the ratio may be less 



