BIOLOGY OF EGGS AND IMPLANTATION 



823 



plying a host of techniques to chirify the 

 physiology of the oviducts. 



The normal functional state of the ovi- 

 ducts is dependent on the maintenance of a 

 delicate balance between estrogen and pro- 

 gesterone. In the mated mouse and rabbit, 

 injections of estrogen result in tube-locking 

 the ova for as long as 7 days after copula- 

 tion, at which time the eggs degenerate 

 (Burdick and Pincus, 1935; Burdick, Whit- 

 ney and Pincus, 1937). By contrast, the in- 

 jection of progesterone (Alden, 1942c) and 

 induced superovulation (Wislocki and Sny- 

 der, 1933) accelerate the passage of eggs. 

 Fertilized ova introduced into the oviducts 

 of pseudopregnant rabbits will continue to 

 develop normally but they are not trans- 

 ported into the uterus. Similarly the eggs of 

 donor rabbits will not be transported if they 

 are introduced into the oviducts of estrous 

 females in which there is no luteal growth 

 (Austin, 1949b). Alden (1942c) carefully 

 removed the ovaries from the periovarial 

 sacs in mated rats and observed the position 

 and development of ova. Ovariectomy after 

 ovulation did not prevent the normal de- 

 velopment or transport of the eggs through 

 the oviduct and, in fact, hastened their 

 transport. Noyes, Adams and Walton (1959) 

 ovariectomized rabbits and found that when 

 freshly ovulated eggs from donor females 

 were transplanted into the ampulla of the 

 oviduct, the eggs were transported into the 

 uterus in 14 hours. 



There is very little pertinent information 

 concerning the role of the cilia in moving 

 the ova through the isthmus and intramural 

 portions of the oviduct. Because of the 

 thickness of the muscular wall in these areas 

 it is difficult to observe the activity of the 

 cilia in living specimens even by trans- 

 illumination (Alden, 1942b). Also the num- 

 ber, size, and arrangement of the ciliated 

 cells in the oviduct varies greatly from spe- 

 cies to species. In addition, individual vari- 

 ations within a given species have been de- 

 scribed throughout the reproductive cycle 

 (Sobotta, 1914; Novak and Everett, 1928; 

 Hartman, 1939; Burdick, Whitney and Em- 

 erson, 1942; Odor, 1948). 



The earlier observations of Parker (1928, 

 1931) on the ciliary currents in the opened 

 oviduct of the turtle. Chryseunis picta, have 



recently been repeated and extended by 

 Yamada (1952) to the tortoise, Clemmys 

 japonicus, and the frog, Rana nigromacu- 

 lata. Yamada described a reverse ciliary 

 movement beating toward the ovarian end 

 of the oviduct in both animals. The rate of 

 the descending current was about two times 

 faster than that of the ascending current. 

 In the frog the activities of the cilia cause 

 the eggs to rotate as they descend. This may 

 be an important mechanism for coating the 

 eggs evenly with egg jelly. Crowell (1932) 

 also described a tract of cilia beating to- 

 ward the infundibulum in the oviducts of 

 several species of lizards. It is generally 

 assumed that during the period in which 

 eggs are being transported the oviducts of 

 most mammals undergo a secretory phase, 

 but it is not known what proportion of the 

 fluid within the lumen is contributed by the 

 secretions of the oviduct, the lining of the 

 periovarial sac when present, the follicular 

 fluid, and the peritoneal fluid. Even less is 

 known concerning the chemistry of these 

 fluids. The rabbit, hare, opossum, and pos- 

 sibly the dog and horse present peculiar 

 problems because of the specialized mucous 

 secretions which coat the eggs and form the 

 tertiary membranes. 



The cytology and secretory activity of the 

 epithelial lining of the oviduct have been 

 the subjects of many studies in mammals, 

 but there is little unanimity of opinion re- 

 garding (1) the changes in cellular mor- 

 phology during the cycle, (2) the types of 

 secretions elaborated, and (3) the cyclic 

 variations of the particular secretory prod- 

 ucts which have been identified. In the ovi- 

 ducts of the pig and man both secretory and 

 ciliated cells are present in the same pro- 

 portions in all phases of the cycle. The 

 height of the ciliated cells varies periodi- 

 cally, reaching a maximum during the time 

 the eggs are passing through the tubes 

 (Snyder, 1923, 1924; Novak and Everett, 

 1928; Bracher, 1957). Allen (1922), among 

 others, expressed the view that there are no 

 ciliated cells in the isthmus of the oviduct 

 of the mouse or rat. This interpretation 

 must be modified at least for the rat, in 

 view of the findings of Alden (1942b), Kel- 

 log (1945), and Deane (1952) that both 

 ciliated and secretory cells are present in 



