818 



SPERM, OVA, AND PREGNANCY 



which they are kept. When the eggs are shed 

 from the follicles they are ordinarily sur- 

 rounded by a variable number of layers of 

 granulosa cells and a matrix of more or less 

 viscid follicular fluid. The vitellus does not 

 completely fill the zona pellucida, and the 

 first polar body, if it has not already disinte- 

 grated, may be pressed between the zona 

 and the ooplasmic membrane. An exception 

 to this may be found in the Canidae in 

 which formation of the first polar body is 

 apparently delayed for some time after ovu- 

 lation. The length of time that the coronal 

 cells persist varies greatly in the eggs of dif- 

 ferent species. 



A well developed corona radiata is regu- 

 larly found in newly ovulated ova of the 

 mouse (Lewis and Wright, 1935), the ham- 

 ster (Ward, 1946), the rat (Gilchrist and 

 Pincus, 1932), the rabbit (Gregory, 1930), 

 the cat (Hill and Tribe, 1924), the dog 

 (Evans and Cole, 1931) , the monkey (Lewis 

 and Hartman, 1941), and man (Hamilton, 

 1944; Shettles, 1953). The rapid dispersal 

 or even absence of the cells forming the 

 corona radiata has been reported for the 

 sheep (McKenzie and Terrill, 1937), the 

 cow (Evans and Miller, 1935; Hamilton 

 and Laing, 1946; Chang, 1949b), the pig 

 (Corner and Amsbaugh, 1917; Heuser and 

 Streeter, 1929), the horse (Hamilton and 

 Day, 1945), and the deer (Bischoff, 1854), 

 and would seem to be a characteristic of the 

 newly ovulated guinea pig ovum (Myers, 

 Young and Dempsey, 1936). 



The eggs of unmated females gradually 

 lose their investment of granulosa cells as 

 they pass through the oviducts. The cells be- 

 come rounded and drop away from the cum- 

 ulus, a process that occurs first in the more 

 peripheral cells. The cells of the corona ra- 

 diata which are adjacent to the zona pellu- 

 cida are the last to fall away and when 

 they are brushed from the surface of the 

 zona in living eggs in vitro their long and 

 irregularly shaped protoplasmic processes 

 extending into the zonal canaliculi can be 

 seen (Squier, 1932; Duryee, 1954; Shettles, 

 1958). The mechanism which effects the dis- 

 persal and final dissolution of the cumulus 

 oophorus and corona radiata in unmated fe- 

 males is not known. It has been suggested 

 that an enzyme, elaborated by the tubal 

 mucosa, is responsible for the dispersal of 

 the cells (Shettles, 1958). 



When an observer follows the cytologic 

 changes in the cells forming the cumulus 

 oophorus as ovulation approaches and notes 

 their behavior in tissue culture preparations 

 in vitro he is impressed with the suggestion 

 that separation of the cells involves a grad- 

 ual depolymerization of the intercellular 

 cement substance and a change in the ac- 

 tivity of the cell surface. 



If time-lapse photographs are made of 

 the coronal cells surrounding ovulated eggs, 

 a very active bubbling and "blister" forma- 

 tion of the surface membranes is apparent. 

 "Bubbling" activity of the cell surfaces is 

 frecjuently seen in cells which are losing 

 their vitality (Zollinger, 1948). These sur- 

 face changes occur at the time when the 

 cells are undergoing most active separation 

 and accounts for the withdrawal of the cyto- 

 plasmic processes from the zona pellucida. 

 Further evidence that the behavior of the 

 cell is related to loss of vitality is shown by 

 their very poor growth in tissue culture. 



F. RESPIRATORY ACTIVITY OF 

 MAMMALIAN EGGS 



There have been only limited investiga- 

 tions on the energy-yielding mechanisms 

 and energy-requiring processes of the de- 

 veloping eggs of mammals (rat, Boell and 

 Nicholas, 1948; rabbit, Smith and Kleiber, 

 1950, Fridhandler, Hafez and Pincus, 1957; 

 and cow, Dragoiu, Benetato and Oprean, 

 1937). 



The fertilized ovum during its various 

 stages of cleavage and differentiation is an 

 ideal experimental object for such studies 

 and has been used extensively in the inver- 

 tebrates, amphibia, and birds where large 

 numbers of eggs are readily available (Bo- 

 ell, 1955). Refinements in the Cartesian 

 diver technique have made possible the 

 measurement of gas exchange of less than 1 

 mfxi.; thus the number of mammalian eggs 

 required to obtain significant data need not 

 be large (Sytina, 1956). Furthermore, the 

 effectiveness of gonadotrophins in inducing 

 ovulation in the sexually immature female 

 rodents and their willingness to mate after 

 such treatment provides a ready source of 

 eggs independent of ovulation at specific 

 phases of the sexual cycle. 



The type of information which can be ob- 



