160 THE DEVELOPMENT OF THE GAMETES OR SEX CELLS 



some of the Golgi substance be identified as myelin figures which develop 

 "at the expense of lipid inclusions." Thus it may be that the Golgi substance 

 which Brambell observed (fig. 89B) passing from the follicle cells to the 

 oocyte represents lipid substance. In the growing oocyte of the rat, Leblond 

 ('50) demonstrated the presence of small amounts of polysaccharides in 

 the cytoplasm of the oocyte, while the surrounding zona pellucida and follicle 

 cells contained considerable quantities.' These considerations suggest that the 

 blood stream using the surrounding follicle cells as an intermediary may con- 

 tribute food materials of a complex nature to the growing cytoplasm of the 

 oocyte. 



The localization of the yolk toward one pole of the egg is one of the move- 

 ments which occurs during fertilization in many teleost fishes. In these forms, 

 the deutoplasmic materials are laid down centrally in the egg during oogenesis, 

 but move poleward at fertilization (fig. 122). A similar phenomenon occurs 

 also during fertilization in Amphioxus and Styela among the protochordates. 

 In many other fishes and in the amphibia, reptiles, birds, and monotrematous 

 mammals, the yolk becomes deposited or polarized toward one pole of the 

 oocyte during the later stages of oocyte formation, as the cytoplasm and the 

 germinal vesicle move toward the other pole (figs. 68H, 72F). The polariza- 

 tion of the deutoplasmic substances thus is a general feature of the organi- 

 zation of the chordate egg. 



3) Invisible Morphogenetic Organization Within the Cytoplasm of the Egg. 

 Two general categories of substances are developed within the cytoplasm of 

 the oocyte during its development within the ovary, viz.: 



( 1 ) the visible or formed cytoplasmic inclusions, and 



(2) an invisible morphogenetic ground substance. 



The former group comprises the yolk spherules, fats, and other visible, 

 often pigmented bodies which can be seen with the naked eye or by means 

 of the microscope. The morphogenetic ground substance probably is com- 

 posed of enzymes, hormones, and various nucleocytoplasmic derivatives en- 

 meshed within the living cytoplasm. However, although we may assume that 

 the basic, morphogenetic ground substance is composed of enzymes, hor- 

 mones, etc., the exact nature of the basic substance or its precise relationship 

 to the various formed inclusions of the cytoplasm is quite unknown (see 

 Fankhauser, '48, for discussion). More recent experiments demonstrate that 

 the yolk or deutoplasmic material not only serves as a reservoir of energy 

 for embryonic development but also is in some way connected with the 

 essential, basic organization of the egg. 



Although we know little concerning the exact nature of the morphogenetic 

 organization of the egg or how it forms, studies of embryological development 

 force upon us but one conclusion, to wit, that, during the period when the 

 oocyte develops in the ovary, basic conditions are elaborated from which the 



