1905.] the Interstitial Cells of the Ovary in the Rabbit. 45 



transverse section is less marked; there are also in many cases fewer 

 follicles in an advanced condition than in the non-pregnant state. Just 

 at this period the energies of the gland have apparently heen directed rather 

 to the formation of the lutein tissue than new follicles. 



From the fourteenth to the eighteenth day the corpora lutea remain at 

 their maximum, and then begin to diminish rapidly in size. Instead of 

 being very vascular whitish bodies, projecting in many cases to the extent 

 of three-quarters of their whole extent beyond the surface of the gland, 

 they gradually diminish both in size and vascularity, until by about the 

 twenty-second day of pregnancy they are merely elevations on the surface, 

 showing the faintest possible trace of vascularity ; this diminution continues 

 steadily until, a little while before birth, the locality of these striking 

 features of the fourteenth day of pregnancy is only seen by the presence of 

 an opaque whitish circular area upon the surface of the ovary. The changes 

 are so marked that it is possible after a little experience to diagnose very 

 approximately the previous duration of the pregnancy from the appearance 

 of the corpora lutea. 



Whilst these external changes are taking place in the lutein tissue, the 

 rest of the ovarian tissue has been also undergoing changes, which, if not 

 so striking in appearance, are none the less evident. It has already been 

 stated that the organ at the fourteenth day shows marked increase in size 

 apart from the corpora lutea ; whereas, shortly after this period, these bodies 

 begin to diminish in size, the reverse takes place in the rest of the ovarian 

 tissue ; and whereas growth of the ovary as a whole has been slow up to the 

 present, it now becomes rapid and continues until close upon the time of 

 parturition. 



By about the eighteenth or twentieth day all trace of wedge-shape in 

 cross-section has completely gone, and the organ is nearly circular, the girth 

 is much greater, and this increase extends right up to the poles. These 

 changes become more and more marked, until at about the twenty- sixth day 

 the organ is well over an inch in length, sometimes about \\ inches, showing 

 a proportionate increase in its other measurements, and having a shape very 

 much resembling a spindle with blunted ends. The number of clear round 

 spots has meanwhile been increasing rapidly, so that in the majority of 

 cases the greater part of the surface is taken up either by them or by the 

 round whitish patches, which mark the spots where the corpora lutea have 

 been projecting above the surface. The formation of follicles appears to be 

 somewhat inhibited during the rapid growth of the corpora lutea, but to 

 be resumed with greater energy when these have reached their maximum 

 development. At the time of parturition there are a large number of 



