METABOLIC AND OTHER CHANGES AT FERTILIZATION 83 



(2.8) Intracellular distribution of ^-P before and after f. L. 

 pictus (Whiteley, 1949). 



When the egg is centrifuged (E. B. Harvey, 1941), it separates into 

 two fragments: a large light part containing an oil cap, a small hyaline 

 layer, the nucleus or mitotic figure and yolk; and a smaller heavier 

 part, containing mitochondria and an optically empty layer. In un- 

 fertilized eggs which have been allowed to accumulate ^^P for six 

 hours, there is 1-2 times as much ^-P in the light, as in an equal 

 volume of the heavy part. In fertilized eggs, the ratio (^^P light) /(^-P 

 heavy) = 0-5, implying that a good deal of the P goes into the mito- 

 chondria, about 20 minutes after fertilization. This paper contains a 

 review of the work on P metabolism in eggs up to 1949. 



(3) Readily exchangeable K, 20% of total in u. eggs; 80% in f. 

 eggs. S. purpuratus (Chambers et al., 1948*). 



(3.1) K exchange 16 times faster in f. than in u. eggs. S. pur- 

 puratus (Chambers, 1949*). 



(3.2) Cyclical changes in K permeability after f. Uptake, o-io 

 min. ; release, 10-40 min.; uptake, 40-60 min. 60% of K in eggs 

 non-exchangeable. P. lividus, A. lixula (Monroy-Oddo & Esposito, 



1951)- 



These results are statistically significant. 



(4) Bound Ca decreases at f. A. punctulata (Heilbrunn et al., 

 1934; Mazia, 1937). 



(4.1) Ca diffuses out of eggs at f . P. lividus (Orstrom & Orstrom, 

 1942). 



(4.2) Ca and Mg diffuse out of eggs at f. (first measurements 

 15 min. after f.). A. lixula (Monroy-Oddo, 1946). 



Lindvall & Carsjo (1951) were unable to confirm (4.1) and (4.2) 

 using the eggs of Echinus esculentus; neither were Barnes, Cleland and 

 I (unpublished). The presence of small amounts of jelly, which con- 

 tains Ca, round unfertilized eggs, may be a confusing factor in experi- 

 ments of this type. The uptake of Ca by sea-urchin egg jelly has been 

 described by Rudenberg (1953); (4-i) and (4.2) should not be 

 accepted unless they are confirmed. There is a further discussion of 

 the role of Ca in fertilization in chapter 8. 



(5) The following changes in inorganic constituents occur at f. 



