OF THE VERTEBRATE OVARY. 595 



dog solid columns are present in the embryo, but later they 

 appear frequently to acquire a tubular form, and a lumen. Pro- 

 bably there are great variations in the development of the tissue, 

 since in the cat (not as Waldeyer did in the dog) I have found it 

 most developed. 



In the very young embryonic ovary of the cat the columns 

 are very small and much branched. In later embryonic stages 

 they are frequently elongated, sometimes convoluted, and are 

 very similar to the embryonic tubuli seminiferi. In the young 

 stages these columns are so similar to the egg tubes (which 

 agree more closely with Pfliiger's type in the cat than in other 

 forms I have worked at) that to any one who had not studied 

 the development of the tissue an embryo cat's ovary at certain 

 stages would be a very puzzling object. I have, however, met 

 with nothing in the cat or any other form which supports 

 Kolliker's views. 



My next stage is that of a twenty-two days' embryo. Of this 

 stage I have given two figures corresponding to those of the 

 earlier stage (figs. 36 and 36 A). 



From these figures it is at once obvious that the germinal 

 epithelium has very much increased in bulk. It has a thickness 

 o - i O'O9 mm. as compared to 0*03 mm. in the earlier stage. 

 Its inner outline is somewhat irregular, and it is imperfectly 

 divided into lobes, which form the commencement of structures 

 nearly equivalent to the nests of the Elasmobranch ovary. The 

 lobes arc not separated from each other by connective tissue 

 prolongations ; the epithelium being at this stage perfectly free 

 from any ingrowths of stroma. The cells constituting the ger- 

 minal epithelium have much the same character as in the previous 

 stage. They form an outer row of columnar cells internal to 

 which the cells are more rounded. Amongst them a few large 

 cells with granular nuclei, which are clearly primitive ova, may 

 now be seen, but by far the majority of the cells are fairly 

 uniform in size, and measure from o - oi O'O2 mm. in diameter, 

 and their nuclei from 0004 croo6 mm. The nuclei of the 

 columnar outer cells measure about crooS mm. They are what 

 would ordinarily be called granular, though high powers shew 

 that they have the usual nuclear network. There is no special 

 nucleolus. The rapid growth of the germinal epithelium is due 



