MATURATION OF GAMETES 159 



On the other hand, the interpretation and description of the yolk body 

 and its subsequent activities given by Brambell ('25) present a different 

 view. According to the latter author, the yolk body is composed entirely of 

 mitochondria; the Golgi substance and centrosphere are absent. Yolk forma- 

 tion proceeds as follows: As the young oocyte grows, the mitochondria in- 

 crease in number and form the mitochondrial cloud (fig. 87A, B). The transi- 

 tory mitochondrial yolk body differentiates within this cloud (fig. 87C). The 

 mitochondrial yolk body ultimately breaks up into a mass of mitochondria, 

 and the latter becomes dispersed in the cytoplasm of the oocyte (figs. 68F, 

 G; 87D). Some of these dispersed mitochondria transform directly into yolk 

 spheres (figs. 68H, 88, 89). Following this, another kind of yolk is formed 

 in vacuoles surrounding these original yolk spheres (figs. 68H, 89A, yolk 

 spheres plus vacuoles). The fat droplets (C-yolk) within the ooplasm are 

 formed according to Brambell "possibly under the influence of Golgi elements" 

 (fig. 68H, fat droplets). Relative to the function of the yolk nucleus and its 

 mitochondria, Brachet ('50), p. 57, considers it significant at the beginning, 

 but its real importance is still to be understood. 



The relationship, if any, of the oocyte nucleus to the deposition of yolk 

 materials is not apparent. One must not overlook the real probability that 

 the germinal vesicle (i.e., the enlarged nucleus of the oocyte) may be related 

 to the increase and growth of the cytoplasm and to yolk formation, for it is 

 at this time that the chromatin threads surrender their normal diplotene 

 appearance and become diffusely placed in the germinal vesicle. They also 

 lose much of their basic chromatin-staining affinities while the Feulgen reac- 

 tion is diminished (Brachet, '50, p. 63). With regard to the possible function 

 of the germinal vesicle in yolk synthesis, the following quotation is taken from 

 a publication by Brachet ('47): 



It is well worth pointing out that Duspiva (1942), using a very delicate and 

 precise technique, found no correlation between the dipeptidase content of the 

 nucleus and the onset of vitellus synthesis: such a correlation exists, however, in 

 the case of the cytoplasm where dipeptidase increases markedly when the first yolk 

 granules make their appearance. These results suggest that there is not evidence 

 that the nucleus is the sit,e of an especially active metabolism; cytoplasmic dipep- 

 tidase probably plays a part in yolk protein synthesis; if the nucleus controls such 

 a synthesis, it works in a very delicate and still unknown way. 



However, the means by which protein synthesis is effected still is a problem 

 which awaits explanation (Northrop, '50). (The interested student should 

 consult Brachet, '50, Chap. Ill, for a detailed discussion of the cytochem- 

 istry of yolk formation.) 



Another aspect of the problem of cytoplasmic growth and differentiation 

 of the oocyte presents itself for further study. Brambell ('25) concluded from 

 his observations that Golgi substance passes from the follicle cells into the 

 ooplasm of the growing bird oocyte and contributes to the substance of the 

 peripheral layer (fig. 89B). Palade and Claude ('49) suggest that at least 



