1905.] the Interstitial Cells of the Ovary in the Rabbit. 44 



reach the ripe state, since they will burst if impregnation occur, whereas 

 this is probably not the case in the immature ovary. There would then, on 

 this view of the case, be no ovulation except in the impregnated rabbit. It 

 is quite possible that the additional stimulus of impregnation may hasten 

 the bursting of the follicle, but it seems somewhat unlikely that without 

 impregnation there should never be ovulation. 



The changes resulting in the production of " heat " are obviously those 

 preparatory to a possible pregnancy. Fertilisation appears to be in itself 

 a stimulus, and sets up general hypertrophy of the entire genital apparatus, 

 producing likewise an improved condition of the animal ; as to the mechanism 

 of the production of this hypertrophy, however, our knowledge may be said 

 to be nil, and we are reduced to classifying the whole as the changes brought 

 about by the stimulus of pregnancy. 



Naked Eye Changes. Fraenckel describes and figures very accurately the 

 naked eye changes in the pregnant ovary of about the fifteenth day in his 

 paper on the function of the corpus luteum. 



These changes are very striking, and indicate in themselves some very 

 definite alteration or increase in the function of the gland ; apart from the 

 formation of the corpora lutea, there is an immense increase in absolute 

 size, the gradual occurrence of which will now be described. 



The ovary of the non-pregnant rabbit is a small yellowish body, lying 

 on either side against the posterior abdominal wall, a little below the kidney. 

 It is usually about ^ inch in length and thin, being slightly wedge-shaped 

 in transverse section and rather pointed longitudinally at either end ; upon 

 its surface may be seen clear round spots, showing the locality of the larger 

 follicles, some of which, if they are nearly ripe, may even project slightly 

 from the surface. 



The bursting of the follicles and fertilisation lead to the formation of the 

 corpora lutea, the so-called " true " corpora lutea of pregnancy, and the 

 growth of these bodies during the early period are undoubtedly the most 

 characteristic feature in the naked eye appearance of the ovary. If the 

 pregnancy be one with a large number of fcetuses, the ovary often looks 

 gnarled, so large and numerous are the excrescences produced upon its 

 surface by these bodies. If these, however, be cut off, and if the organ be 

 carefully examined at about the fourteenth day, when the corpora lutea are 

 at their maximum state of development,* it will be readily seen that the 

 ovary itself has increased in size, quite apart from the formation of the 

 liitein tissue. The whole gland has a more swollen and rather less compact 

 aspect ; it is larger both in length and girth, and the wedge-shape of the 



* Cf. .Fraenckel, loc. cit. 



