CHAPTER IX 



THE GROWTH AND IMPLANTATION OF THE 

 BLASTODERMIC VESICLE 



In the cinematographs of Lewis and Gregory (1929) the 

 regular cleavage of rabbit ova in vitro is shown to occur at 

 approximately the same rate as in vivo and the formation of 

 the blastocyst is initiated. The rapid expansion of the 

 blastocyst into the typical large blastodermic vesicle (see 

 Plate VII, Fig. 21) does not, however, occur. The attempted 

 expansion is apparently barred by the presence of the rela- 

 tively rigid zona pellucida and albumen coating so that the 

 blastocyst alternately expands and collapses over a period 

 of many hours until degeneration finally ensues. Br ache t 

 (1912, 1913) had previously shown that ova recovered from 

 the uterus of the rabbit at 5 to 6 days after coitus will 

 develop normally for 24 hours to 48 hours, passing from 

 the tridermic stage to the stage of the primitive streak, 

 with normal development of the ectoplacenta. Rabbit ova 

 enter the uterus between 72 and 75 hours after copulation 

 (Cruikshank, 1797; Assheton, 1894; Gregory, 1930) in the 

 early blastocyst stage and still surrounded by the zona 

 pellucida and the albumen coat. There is a rapid expansion 

 of the ovum at this time due to the infiltration of fluid into 

 the vesicle cavity so that by 96 hours after copulation the 

 blastocyst is easily three times the diameter of the tubal 

 egg. Very soon after the entry of the ovum into the uterus 

 the viscosity of the stretched albumen layer appears to 

 decrease so that its persistence about the large pre-primitive 

 streak vesicle of the 6th day must be due to a marked soften- 

 ing. By the end of the 6th day to the 7th day it disappears 

 completely due probably to its digestion by uterine fluids 

 since it does not disappear in culture-grown ova. The growth 



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