II GAMETOGENESIS AND FERTILIZATION 721 



in ting the formation of antibodies, and although not all adult antigens and 

 haptens are demonstrable in the egg by the usual techniques, at least some 

 antigens (or their combining groups) of the egg are identical with or closely 

 related to those of the adult." The discussion in this paper is particularly useful 

 for review of problems concerning molecular differentiation as well as identity 

 in successive stages of development. Using the Oudin (1948) technicjue, Cooper 

 (1950) identified "5-7 antigens in the egg and neural plate stages which are 

 represented by substances with immunologically related combining groups in 

 adult frog serum". 



In spite of the precision of antigen-antibody reactions, caution still must be 

 exercised with regard to conclusions of serological identity of maternal and yolk 

 proteins. Fevold (1951) in a comprehensive review states that "no protein of egg 

 yolk has been shown to have been isolated in pure form by the criteria currently 

 applied". He describes the composition of vitellin, livetin and phosvitin, as well 

 as other egg proteins, and points out the fact that livetin apparently contains the 

 majority of enzymes of the egg. Lineweaver et al. (1947) associated tributyrinase, 

 esterase, amylase, peptidase, phosphatase and catalase activity with livetin. 



{b) Cleavage and blastulation 



During the period of cleavage, growth is slight. Protein metabolism studies 

 may, therefore, be of interest in a negative sense. Brachet (1939) observed only 

 a slight nitrogen excretion in the form of ammonia and urea through the neuru- 

 lation stage (amphibia), and felt that this observation corroborated those of 

 Bialaszewicz and Mincowna (1921). The fact that ammonia excretion increased 

 under anaerobic conditions, he felt, favored the hypothesis that ammonia might 

 be used in the presence of oxygen for synthesis of amino acids and proteins. 

 Barth and Barth (1954) point out that "cleavage and blastulation of the frog egg 

 are accompanied by a steadily increasing rate of respiration. As yet there is no 

 conclusive evidence as to the nature of the compound oxidized. Direct chemical 

 analyses of the lipid, carbohydrate and protein show no significant changes 

 between fertilization and the beginning of gastrulation". They further conclude 

 from analysis of the extensive study of Gregg and Ballentine (1946) that, since 

 only traces of ammonia and urea are present, only traces of protein catabolism 

 can occur. It should be added, however, that Gregg and Ballentine did not study 

 excreta from the embryos, and much of the cogency of the Barths' position is 

 thereby nullified. A similar confusion exists from the data of Wills (1936) which 

 show, for different species of amphibia, a range from — 12.5% to +13.3% in 

 total nitrogen of the gastrula as compared with the egg. 



In the sea urchin, careful studies have been made and indicate a somewhat 

 greater activity of the nitrogen compounds. Kavanau (1953) describes a loss in 

 protein nitrogen of 15.7% and of nonprotein nitrogen of 29.1% (See Fig. 2). 

 The loss of total amino-acid nitrogen (18.7%) represents a conversion to other 

 nitrogen fractions as well as combustion for energy. In the former connection, 

 Abrams (1951) confirmed conversion of glycine to purines. Similarly Gustafson 

 and Hjelte (1951) reported a conversion of 5.7% amino-acid nitrogen into other 

 fractions prior to the i8-h. stage. 



Literature p. 744 



