VESICLE GROWTH AND IMPLANTATION 115 



a whole has gone through a primary torsion, separating it 

 from the embryonic membranes in the region of the intestinal 

 portal and contributing to its apparent reversal of posture. 



"The total growth attained in the 48 hour period is less 

 than half that attained by the normal embryo during the 

 same period. The maximum differentiation is nearly three- 

 quarters of that undergone by the normal. The factors 

 limiting growth are affected earlier than those limiting 

 differentiation. 



'^ Apparently respiratory interchange is the most important 

 functional necessity at this stage. The efficiency of this 

 mechanism is not only lowered by the total absence of 

 maternal circulation but even further prevented by the 

 growth of a new enveloping membrane in the nature of a 

 decidua from the marginal cells of the ectoplacental cone. 

 The accumulation of break-down products due to metabolic 

 activity is another checking factor. A few preliminary 

 experiments have shown that these can be removed by 

 washing the entire culture in sterile Ringer's solution and 

 adding fresh embryonic extract. By using this method 

 embryos have been kept alive for 96 hours although growth 

 and differentiation occur only at a low rate during the last 

 24 hours." 



Nicholas (1934) has also observed a few cases of the 

 development of rat embryos from ova dropped into the 

 uterine cavity, and extra-uterine pregnancies in man are of 

 course well known. In the rat the removal of the entire 

 gestation sac from the uterus into the peritoneal cavity 

 may be performed without hindering fairly advanced em- 

 bryo development in the extra-uterine environment (Selye, 

 Collip and Thomson, 19356).^ It therefore appears that 

 some somatic influence carries the ova through the critical 

 early blastocyst stages and that this influence does not 

 operate in the ordinary tissue culture media. 



It will be recalled that this critical stage occurs at the 

 time of the disappearance of the egg envelopes and Hall 

 (1935) has recently presented data offering a possible clue 



