ORGANIZING ASPECTS OF GAMETOGENESIS 



313 



C d 



Fig. 7. Secondary vitellogenesis in Amphibians, (a) Xenopus oocyte (Zenker, Unna-Brachet 

 stain) : the section is probably sagittal, on the animal side of the nucleus; a basophilic zone, 

 where secondary vitellogenesis begins is visible; (b) Part of a frog oocyte (Bouin, trichrome) 

 showing from bottom to top the nuclear content, the deeply folded nuclear membrane, the 

 perinuclear production of small platelets, and the primary yolk; (c) the nuclear zone of 

 a newt oocyte (Zenker, Azan) : the large nucleus appears clear in the dark background of 

 yolk; in the center, chromosomes (grey) and a swarm of central nucleoli; at the periphery, 

 other nucleoli against the membrane; (d) Same material and technique: detail of the 

 scattered nucleoli inside the nuclear membrane. From Wittek. 1952. 



cannot, of course, be found. Polarization results from the location of paraplasm 

 or deutoplasm on the side of the nucleus where the centriole and Golgi system 

 are combined with much RNA (Fig. 3). This complex called the yolk nucleus, 

 is less an organ of yolk elaboration than a structure controlling the location of 

 yolk (Chandhry, 1952). In the teleost Lebistes, a definite change of polarity takes 

 place during the growth of the oocyte. The germinal vesicle first lies in the region 

 farthest from the ovarian hilus; during the late period of vitellogenesis, the vesicle 

 gradually moves nearer to the hilus and consequently the axis turns through an 

 angle of 90^ (fig. 9). The cause seems to be the unilateral formation of a special 

 plasm containing large granules (V^akaet, 1955). For amphibian oocytes', it has 



' The relative content of newt oocytes in RNA and proteic components at the successive 

 stages of growth has been estimated by Osawa and Hayashi (1953). The young cell is first 

 loaded with RNA, but the synthesis of ribonucleoproteins is soon largely surpassed by the 

 formation of new cytoplasm and yolk. 



Lilerulure />. 483 



