METABOLIC AND OTHER CHANGES AT FERTILIZATION 85 



(9.3) Surface of oi! droplets Feulgen-negative in u. eggs and 

 Feulgen-positive in f. eggs. A'', succinea (Lovelace, 1949*). 



This experiment requires confirmation. A Feulgen-positive re- 

 action in the presence of lipids is a common artifact. However, 

 Costello (1938) found that the oil droplets can be made to coalesce 

 after fertilization, but not before, in eggs of the same species. 



(9.4) Doubling of DNA content of pronuclei after f. and before 

 fusion. M. differ entialis, P. variegatus, M. musculus (Swift, 1953; 

 Swift, unpubl.). 



(9.5) Appearance of RNA 'granules' in the cytoplasm of the 

 spermatozoon and their dispersion in the egg cytoplasm by the end 

 of maturation. A. equorum (Panijel, 1947; Pasteels, 1948). 



(9.6) 'Dissolution' of Ascaridin, previously surrounding the 

 sperm head. A. equorum (Pasteels, 1948). 



Note on (9.i)-(9.6). The problem of RNA and DNA variations and 

 their inter-relationship in eggs and spermatozoa is extremely compli- 

 cated, if not confused ; the non-specialist might be wise to wait a few 

 years before tackling this question. Pasteels & Lison (1951) for 

 example, made a detailed examination of the DNA content of the eggs 

 and spermatozoa of SabeUaria alveolata. Contrary to expectation, 

 they claimed first, that the DNA content of eggs and spermatozoa was 

 not the same ; and secondly, that the DNA content of diploid cells was 

 not double that of haploid cells, the ratio being i : 12 in the case of 

 spermatozoa compared with the first blastomere, and i : 5-5 in the 

 case of the mature egg compared with the first blastomere. After 

 fertilization, Pasteels & Lison found that DNA was synthesized in the 

 male pronucleus, its content increasing by a factor of 6. The factor 

 for the egg during this period was 2-75. Further information will be 

 found in a paper by Alfert & Swift (1953), who could not confirm the 

 results of Lison & Pasteels; in a review by Swift (1953); and in a 

 paper by Hoif-Jorgensen (1954), who reported that the total DNA 

 content of sea-urchin eggs {Paracentrotus lividus) and of frogs' eggs 

 (Rana temporaria Linn.) remained constant for a considerable time (3 

 and 18 hours, respectively) after fertilization. 



(9-7) D-usnic acid inhibits the fusion of the male and female pro- 

 nuclei, though they approach each other in the usual way. It also 

 inhibits cleavage and the uptake of ^^P, though Og uptake is un- 

 affected. A. punctulata (Marshak & Fager, 1950). 



