BIOLOGY OF EGGS AND IMPLANTATION 



801 



the vagina and cervix has usually failed to 

 result in pregnancy (Dowling, 1949; Um- 

 baugh, 1949; Rowson, 1951). Two excep- 

 tions have so far been reported. Kvasnickii 

 (1951) obtained one pregnancy in the sow 

 from eggs placed in the uterus per vaginam 

 and Beatty (1951) obtained 5 young from 

 55 mice morulae and blastulae introduced 

 into the cornua by the same approach. Since 

 the normal development of ova in artificial 

 pregnancy is wholly dependent upon the 

 environment into which they have been 

 placed, day-old rabbit ova would develop 

 into normal young only when transferred 

 to oviducts of animals in which ovulation 

 had been induced at approximately the same 

 time. Similarly, blastocysts would develop 

 into young only when transplanted into 2- 

 day or 5-day cornua (Chang, 1950c). Again 

 in transferring fertilized tubal ova to the 

 cornua of rats, Nicholas (1933) reported 

 that when the host animal ovulated later 

 than the donors, implantations were greatly 

 reduced as compared to those instances in 

 which the cycles were more closely synchro- 

 nized. Dickmann and Noyes (1960) trans- 

 ferred ova that were one day younger than 

 the cornua to host females and found that 

 they developed at a normal rate until the 

 fifth day, when they degenerated and failed 

 to implant. On the other hand, ova that were 

 one day older than the host's cornua delayed 

 their development until the endometrium 

 had "caught up" and was ready for im- 

 plantation. This implies that there is a very 

 critical egg-uterine interrelationship that is 

 established on the fifth day of pregnancy in 

 the rat. Transplantation of rat ova beneath 

 the kidney capsule (Nicholas, 1942) and of 

 mouse ova into the abdominal cavity and 

 anterior chamber of the eye (Fawcett, Wis- 

 locki and Waldo, 1947; Runner, 1947) have 

 resulted in only partial embryonic develop- 

 ment. 



D. THE PRODUCTION OF EGGS 

 BY SUPEROVULATION 



Many studies have been directed to meth- 

 ods for superovulating various animals, then 

 fertilizing the eggs in vivo, recovering and 

 transferring them to recipient females 

 (Clewe, Yamate and Noyes, 1958; Noyes, 

 1952; and Chang, 1955a). 



Sucli possibilities have been realized es- 



Fk;. 14.2. Result of autotransfer of a 4-cell goat 

 egg, B. Tlio mother was operated upon on the sec- 

 ond day after breeding, the oviduct was removed 

 and the 4-cell egg (A) was washed out. The egg 

 was then injected into the opposite horn of its 

 mother (Warwick and Berry, 1949). 



pecially by Chang (1948a), who obtained 

 53 2-celled rabbit ova from a single doe. 

 These ova were transplanted to 4 other fe- 

 males and yielded 45 normal young. Using 

 somewhat similar techniques of superovula- 

 tion and in vivo fertilization in rabbits, Avis 

 and Sawin (1951) obtained 81 per cent suc- 

 cessful impregnations and Dowling (1949) 

 78 per cent pregnancies. 



Subsequently, Marden and Chang (1952) 

 performed the novel experiment of shipping 

 superovulated, fertilized rabbit ova by way 

 of aerial transport from Shrewsbury, Massa- 

 chusetts, to Cambridge, England, for suc- 

 cessful transplantation into recipient does. 

 While in transport, the eggs were stored in 

 a flask containing whole rabbit serum kept 

 at temperatures from 12 to 16°C. In domestic 

 animals, the economic importance of such 

 transfer of eggs from genetically superior 

 animals is receiving considerable attention 

 (see Proceedings of the First National Egg 

 Transfer Breeding Conference, 1951). Un- 



