33 Miss J. E. Lane-Claypon. On the Origin, etc., of [June 16, 



streaming inwards from the periphery of some of the cells of the germinal 

 epithelium. 



The changes connected with ovogenesis have been very fully described by 

 v. Winiwarter(19). They may be briefly summarised as follows. The 

 germinal cells of the second invagination are rather small and show a nucleus 

 with some lumps of chromatin, being also rather granular. These he calls 

 protobroque cells of the a variety. These divide, giving rise to other 

 protobroque cells a, and also to a b variety. These last divide again 

 giving rise to more cells of the b variety and to a new form of cell, deuto- 

 broque. The last are larger, and the nucleus more transparent. The deuto- 

 broque cells give 'rise to the ova by nuclear differentiation by means of the 

 following stages. 1. The chromatin breaks up -into fine filaments, which are 

 distributed over the whole nuclear area ; this is the leptotenic stage. 2. The 

 filaments become gradually massed together until they show as a compact 

 lump at one side of the nuclear area. This transformation is the synaptenic 

 stage, which is succeeded by 3, the pachytenic. Here the filaments become 

 again spread out, but they are much coarser than in the previous stages 

 The 4th stage, or diplotenic, is so called on account of the tendency of the 

 chromatin strands to lie in pairs. In the final or dictyate condition the 

 chromatin is distributed in a reticulum over the greater part of the nuclear area 



Balfour describes protoplasmic masses of young ova where the cells appear 

 fused, and he suggests that one of these ova may grow at the expense of the 

 rest. Van Beueden (5) describes multinucleated masses in the ovary of the 

 adult bat, which he suggests may give rise to an ovum and its follicular 

 epithelium. 



The formation of follicles, which proceeds rapidly, gives rise in the ovary to 

 two zones, an external or parenchymatous zone in which the follicles lie, 

 and an interstitial vascular zone ; these have been described with some modi- 

 fications by various workers and for different animals. (His (11), Waldeyer, 

 Born (6), Macleod (13), Van Beneden.) 



The question of the post-natal formation of primordial ova has been the 

 subject of many isolated observations. Pfliiger believed he had evidence of 

 the return of the ovary to the tubular formation at the rutting season, the 

 object of the return being the formation of fresh ova. Waldeyer believed 

 that ail ova were formed in the young animal, and for this reason called all 

 ova " primordial ova." 



Schron noticed an increase in the number of clear cells, presumably ova, 

 near the periphery in cats and rabbits at the rutting season, and in women at 

 the menstrual periods. Koster (12) describes prolongations of epithelium 

 with formation of fresh ova and follicles in the ovaries of several recently 



