598 THE STRUCTURE AND DEVELOPMENT 



The general appearance of the germinal epithelium at this 

 stage certainly appears to me to lend support to my view that 

 the whole of it simply constitutes a thickened epithelium inter- 

 penetrated with ingrowths of stroma. 



The cells of the germinal epithelium, which form the various 

 layers, have undergone important modifications. In the first 

 place a large number of the nuclei at any rate of those cells 

 which are about to become ova have undergone a change 

 identical with that which takes place in the conversion of the 

 primitive into the permanent ova in Elasmobranchs. The 

 greater part of the contents of the nucleus becomes clear. The 

 remaining contents arrange themselves as a deeply staining 

 granular mass on one side of the membrane, and later on as 

 a somewhat stellate figure : the two stages forming what were 

 spoken of as the granular and stellate varieties of nucleus. To 

 avoid further circumlocution I shall speak of the nucleus under- 

 going the granular and the stellate modifications. At a still 

 later period the granular contents form a beautiful network 

 in the nucleus. 



The pseudo-epithelium (fig. 38 A) is formed of several tiers of 

 cells, the outermost of which are very columnar and have less 

 protoplasm than in an earlier stage. In the lower tiers of cells 

 there are many primitive ova with granular nuclei, and others 

 in which the nuclei have undergone the granular modification. 

 The primitive ova are almost all of the same size as in the 

 earlier stage. The pseudo-epithelium is separated from the 

 middle layer by a more or less complete stratum of connective 

 tissue, which, however, is traversed by trabeculae connecting the 

 two layers of the epithelium. In the middle layer there are 

 comparatively few modified nuclei, and the cells still retain for 

 the most part their earlier characters. The diameter of the cells 

 is about O'Oi2 mm., and that of the nucleus about O'OOS mm. 

 In the innermost layer (fig. 38 B), which is not sharply separated 

 from the middle layer, the majority of the cells, which in the 

 previous stage were ordinary cells of the epithelium, have com- 

 menced to acquire modified nuclei. This change, which first 

 became apparent to a small extent in the young two days after 

 birth, is very conspicuous at this stage. In some of the cells the 

 nucleus is modified in the granular manner, in others in the 



