ONE FlQURE
Since the initial work of Markee and Andersen ('34) who demonstrated chapges in area of transplanted endometrium during pregnancy in the rabbit, it has been demonstrated repeatedly that, cycles of growth and regression occur in both transplanted endometrium and in the uterus in situ during the course of pregnancy in the rabbit (Markee and Hinsey, '35 ; Markee, Wells and Hinsey, '36 ; Reynolds, '37 a, b) .2 Narkee and Andersen ( '34) found that intraocular endometrial transplants undergo three distinct cycles of growth and regression during pregnancy, namely, (1) from the day of mating through the fifth day, (2) from the sixth day until the twenty-eighth day, and (3) from the twenty-ninth day until approximately 6 days post-partum. The morphologic changes in uterine tissue accompanying these size changes have not been described and it was the purpose of this study to determine the histologic changes in the uterus in situ that may account for them.
MATERIALS AND PROCEDURE
Fifty-nine of the sixty-three adult female rabbits used in this study received intraocular endometrial transplants after
The author expresses his thanks to Prof. J. E. Markee, Dept. of Anatomy, Stanford University for suggesting the problem and for suggestioiis and criticisms during its execution.
'The term "growth" is nsed to mean increase in size.