810 



SPERM, OVA, AND PREGNANCY 



stained cells, as migrating toward the egg 

 (Gresson, 1933; Moricard, 1933; Aykroyd, 

 1938; Beams and King, 1938; Zlotnik, 1948) . 

 How the yolk material is transferred from 

 the cells of the corona radiata into the egg 

 itself has not been miequivocably demon- 

 strated. A reversal of the polarity of the 

 Golgi complex in the follicular cells of the 

 more mature follicles suggested to Henneguy 

 (1926), Gresson (1933), and Aykroyd 

 (1938.) that it may be responsible, at least 

 in part, for the elaboration of the follicular 

 fluid. 



The appearance and distribution of the 

 mitochondria in the mammalian egg also 

 vary greatly from animal to animal. Rod- 

 like or granular mitochondria have been de- 

 scribed as being concentrated around the 

 Golgi material in the fixed and stained eggs 

 of the dog (Zlotnik, 1948) and in the 

 cortical zones of the eggs of the bat, cat, and 

 dog (Van der Stricht, 1923). In the mature 

 unfertilized eggs of the rabbit, mouse, and 

 hamster the mitochondria are concentrated 

 in the peripheral zones. At the time of fer- 

 tilization they migrate to the region of the 

 developing pronuclei and tend to aggregate 

 around them (Lams, 1913; Gresson, 1940). 



Observations of the living eggs of the rat 

 and guinea pig by time-lapse cinematog- 

 raphy at the time of fertilization do not 

 reveal a significant displacement of the cy- 

 toplasmic inclusions such as have been de- 

 scribed in fixed and stained preparations. 



The ultracentrifuge has been used in an 

 investigation of the cytoplasmic components 

 of the eggs of the mouse and human (Gres- 

 son, 1940; Aykroyd, 1941). In the human 

 ovarian egg coagulated cytoplasm occupies 

 more than one-half of the cell, whereas the 

 nucleus, mitochondria, and Golgi material 

 are confined in the remaining half. During 

 ultracentrifugation the mouse egg is strati- 

 fied into four distinct layers: (1) a cen- 

 tripetal layer, which stains very lightly and 

 which may contain a few small Golgi ag- 

 gregations, (2j a thin layer of yolk, (3) 

 a relatively wide band containing the major 

 portion of the Golgi material and the nu- 

 cleus, and (4) a wider band containing prin- 

 cipally the mitochondria (Gresson, 1940). 



The distribution of nucleic acids in the 

 developing and the mature rat and rabbit 

 egg has been studied histochemically by 



Vincent and Dornfeld (1948),Dalcq (1956), 

 Dalcq and Jones-Seaton (1949), Austin 

 (1952b), Van de Kerckhove (1959); and 

 Sirlin and Edwards (1959). As the oocyte 

 grows, the desoxyribonucleic acid content 

 of the nucleus is reduced and a perinuclear 

 band of ribonucleic acid makes its appear- 

 ance in the cytoplasm. Vincent and Dorn- 

 feld attributed the organization of the pri- 

 mary follicle to the evocating action of the 

 ribonucleic acid elaborated by the oocyte. 

 Alicrophotometric determinations of desoxy- 

 ribonucleic acid (DNx\) have been reported 

 on Feulgen-stained nuclei of mouse oocytes 

 and of cleaving eggs (Alfert, 1950). The 

 data indicate that the amount of DNA 

 {present in a primary oocyte nucleus is con- 

 stant, but that as the nucleus grows the 

 DNA is progressively diluted. On the other 

 hand, just before the first cleavage in fer- 

 tilized eggs the amount of DNA in the 

 pronuclei is doubled. The nuclei of each of 

 the succeeding cleavage stages contain twice 

 the amount of DNA present in the early 

 pronuclei. In addition, studies were carried 

 out on the protein concentration in oocytes 

 and cleavage nuclei using the Millon re- 

 action. The ripe egg contains a reserve of 

 proteins which is divided among the cells 

 and nuclei of the cleavage stages. 



Attention should be directed to the raj)- 

 idly expanding literature dealing with the 

 cytology and biochemistry of the eggs of 

 amphibia and the chick. Clues for experi- 

 mental methodology on the eggs of mam- 

 mals may be found within these rejiorts 

 (Bieber, Spence and Hitchings, 1957; Flick- 

 inger and Schjeide, 1957; Rosenbaum, 1957, 

 1958; Wischnitzer, 1957, 1958; Bellairs, 

 1958; Tandler, 1958; also see Tyler, 1955, 

 and Brown and Ris, 1959). 



The use of compounds labeled with radio- 

 isotopes is an important tool for the study 

 of the transport and utilization of various 

 substances by eggs (^Moricard and Gothie. 

 1955, 1957, Lin, 1956; Friz, 1959). Most of 

 the tracer experiments have been done in the 

 chick and amphibia in which it is clear that 

 such egg storage materials as lecithin, cepha- 

 lin, and vitellin are formed in organs outside 

 the ovary and transported by way of the 

 plasma to the egg. Greenwald and Everett 

 (1959) injected pregnant mice with S^*" me- 

 thionine and subsequently studied the eggs 



