MANIPULATION OF EGGS 111 



embryo, embryos a little in advance of the uterine changes having 

 the best chances. This has been shown in the rabbit (Chang, 1950a, 

 I95id), mouse (Fekete and Little, 1942; Runner and Palm, 1953; 

 McLaren and Michic, 1956), rat (Nicholas, 1933b; Dickmann and 

 Noyes, i960; Noyes and Dickmann, i960) and sheep (Avcrill and 

 Rowson, 1958). Only limited development seems possible in 

 interspecific and intergencric transfers. The transfers tested have 

 been: reciprocally between sheep and goat (Warwick and Berry, 

 1949, 1951; Warwick, Berry and Horlacher, 1934), between sheep 

 and rabbit (Averill, 1956; Averill, Adams and Rowson, 1955), and 

 reciprocally between rabbit, mouse, rat and guinea-pig (Briones and 

 Beatty, 1954). 



Other problems that have been attacked by the egg-transfer 

 technique include : the developmental capacity of eggs from imma- 

 ture rabbits (Adams, 1953, 1954) and mice (Runner and Palm, 1953 ; 

 Gates, 1956; Edwards and Gates, 1959), and of eggs from pseudo- 

 pregnant rabbits (Black, Otto and Casida, 195 1), and the specific 

 effect of the maternal environment upon the characters of the young 

 animal (Fekete, 1947; Fekete and Little, 1942; Venge, 1950; McLaren 

 and Michie, 1958; Green and Green, 1959). Brochart (1954) re- 

 ported that he was able to demonstrate, both with transfer and 

 culture techniques, the survival of some rabbit 2-cell eggs in which 

 the blastomeres had been mechanically separated. There are also 

 problems of a technical nature that have drawn attention, the one 

 of greatest practical importance probably being that of the transfer 

 of early uterine blastocysts between cows without recourse to 

 surgery; a successful procedure has yet to be developed. 



Studies on Eggs maintained in vitro 



Metabolism. Observations on the metabolism of invertebrate eggs, 

 especially of sea-urchin eggs, are numerous and extensive, and 

 consideration of this subject is apt to account for a major part of 

 treatises on invertebrate fertilization and early development (see, for 

 example, Runnstrom, 1949; Brachet, i960). By contrast, very little 

 information is available on the metabolism of mammalian eggs and 

 early embryos, chiefly because they are difficult to obtain in even 

 moderate numbers. A few attempts have been made to determine 

 the oxygen uptake of eggs. Dragoiu, Benetato and Opreanu (1937) 

 made observations on cow eggs with the Warburg apparatus, but 

 their results are of doubtful significance because the eggs they used 



