1905.] the Interstitial Cells of the Ovary in the Rabbit. 37 



inspection shows that there are a few fine processes pushing their way- 

 outwards and more or less enclosing large numbers of germinal cells. The 

 latter are of all shapes and sizes, from the typical protobroque to the deuto- 

 broque type. 



By the third day after birth the general configuration of the ovary has 

 changed very considerably. There is still the central mesoblastic core, but 

 the germinal cells have become more marked off than in the embryo, presenting 

 the appearance of a definite zone of germinal epithelial cells. The cells are 

 arranged, especially in the more central parts of the zone, in the form of solid 

 rods or clusters, several cells thick, which press their rounded ends into the 

 central mesoblast. Some of them might fairly easily be mistaken for tubules 

 without a lumen, and there can I think be little doubt that these are what 

 Pfliiger took for tubules. Around the periphery the tubular formation is not so 

 marked, the cells lying in irregular aggregations (fig. 3). As the mesoblast is 

 centrally situated those parts of the germinal zone lying towards the centre 

 get divided up earlier than the more peripheral parts, which retain the 

 formation of an earlier stage. This lagging behind, as it were, of the periphery 

 is quite characteristic of all the changes taking place in the young ovary ; it 

 applies to the formation of tubules and clusters, to the processes of ovogenesis, 

 as pointed out by v. Winiwarter, as well as to the formation of interstitia 

 cells, which will be dwelt upon later on. 



From this time onwards up to about the twelfth day after birth the changes 

 in the general configuration of the ovary are brought about by an amplification 

 of the processes already described, namely, continued upgrowths of connective 

 tissue, cutting off the tubules and clusters. The connective tissue likewise 

 presses into the larger collections of germinal cells, thus cutting them off and 

 dividing them again into smaller portions, so that as time goes on the clusters 

 near the central parts consist of less cells, but are present in much greater 

 number, while those parts more peripherally situated are in a somewhat 

 earlier stage, the cluster formation being still fairly evident close to the 

 periphery as late as the sixteenth day.* 



Before proceeding to the changes in the egg-clusters about the fifteenth 



* Too much stress, however, should not be laid upon the exact date of the young ovary 

 in relation to its structural aspect. There seems to be an appreciable difference in the 

 extent to which the ovary is developed in different animals about this age. v. Winiwarter 

 does not describe any ovary between, the tenth and the eighteenth day, because he does not 

 consider the changes to be sufficiently striking to call for any description. Of two 

 litters of rabbits I found slight differences in the ovaries of the same date, the sixteenth 

 day, the changes being rather more advanced in one than in the other, and both were 

 almost as advanced as v. Winiwarter's figure of the eighteenth day. The differences are 

 probably determined by the varying nutrition of the animal, as also possibly by the kind 

 of rabbit, some being far more advanced in outward aspect at this age than others. 



