224 Dr. C. Shearer. On the Oxidation Processes of 



As the supply of free energy required by the developing ovum is mainly or 

 entirely derived from its oxidation processes, it is surprising to find that 

 during fertilisation, where a very large amount of energy is immediately 

 rendered available, none of it is liberated as the result of the fusion of the 

 egg pronuclei, a feature which heretofore has always been considered the most 

 essential and important part of the whole process. 



It is of interest in this connection to compare roughly the oxygen con- 

 sumption of the ovum on fertilisation with that of the fixed tissues of the 

 adult body. If we take liver tissue as one in which the metabolic rate is high, 

 according to Barcroft and Shore (6), 1 grm. of fresh liver tissue from a well-fed 

 cat consumes - 024 c.c. of oxygen per minute, which is equivalent to 

 240 c.nim. in 10 minutes. If we take Schryver's (7) figures of the protein 

 nitrogen-content of 1 grm. of well-fed cat's liver as 22-4 mgrm. nitrogen, we find 

 the oxygen uptake of the ovum in the first 10 minutes of the fertilisation 

 process, as compared with that of a similar quantity of liver protein in the 

 same time, is in about the ratio of 13'8 to 10"7 in round figures. In the 

 unfertilised egg this proportion is 0'37 to 10'7 for the same time. 



IV. Discussion. 



There are good reasons for believing, as the result of Loeb's (8) experiments 

 on the fertilisation of the eggs of Strongylocentrotus with the sperm of Asterias, 

 and Lillie's (9) description of the process of fertilisation in Nereis, that the entry 

 of the spermatozoon into the egg consists of two distinct phases. Firstly, an 

 external one, in which certain changes are brought about in the cortical 

 substance of the egg the moment the sperm make contact with the external 

 surface of the egg-membrane ; this would seem to be correlated with the 

 initial oxidation taking place in the egg, as described above for E. micro- 

 tuberculatus. Secondly, the changes following the actual entry of the sperma- 

 tozoon into the egg cytoplasm itself, which, as Lillie has shown in Nereis, only 

 takes place some 30 minutes after the first phase of fertilisation, and in the 

 sea-urchin follows some 10 to 15 minutes after the sperm are added to the 

 eggs. 



By centrif aging the eggs of Nereis before the sperm has actually penetrated 

 the egg-membrane, Lillie was able to separate the jelly surrounding the egg 

 and containing the spermatozoon from the egg itself. These eggs complete 

 meosis, which has been initiated by the spermatozoon, but never segment. A 

 typical segmentation nucleus is, however, formed, which breaks down leaving 

 the chromosomes free in the egg cytoplasm ; they split longitudinally in the 

 normal manner, but never separate. No asters or miotic spindle appear in 

 these eggs, as when the complete process of fertilisation is allowed to take 



