THE ORGANS OF THE MIDDLE GERM-LAYER. 



375 



Fig. 214. Cross section through the ovary of a 

 Rabbit 5 days old, after BALFOUR. Highly 

 magnified. 



k.e, Germinal epithelium ; u.ei, primitive (or 

 primordial) ova ; ei.b, egg-nests ; bi, connec- 

 tive tissue. 



Beneath the germinal epithelium there is to be found, even at that 

 time, embryonic connective tissue with stellate cells (E], which are 

 in an active state of proliferation. In this way there arises on 

 the median side of the mesonephros the ovarian ridge, which is 

 separated from the urinary tubules by a small quantity of embryonic 

 connective substance. 



Changes similar to those of the Chick occur in Mammals, with 

 this difference, that the ger- 

 minal epithelium appears to 

 attain a much greater thick- 

 ness. 



In older stages of develop- 

 ment the boundaries between 

 the germinal epithelium, which 

 is in process of rapid prolife- 

 ration and therefore exhibits 

 numerous figures of nuclear 

 division, and the underlying 

 connective tissue become less 

 and less distinct. This results 

 from the simple fact that a 

 process of mutual ingrowth 

 now occurs bettceen the epithe- 

 lium and the embryonic con- 

 nective tissue (fig. 214). I 

 purposely say a process of 

 mutual ingrowth, for I leave 

 it undetermined whether the 

 germinal epithelium in con- 

 sequence of its development 

 grows into the embryonic con- 

 nective tissue in the form of 

 cords and distinct groups of cells, or whether the connective tissue 

 penetrates with its projections into the epithelium. Probably both 

 tissues are actively engaged in the process. 



In the phenomenon of intergrowth, which continues for a long 

 time during development, two chief stages can be distinguished. 



At first there arise from the germinal epithelium both slender and 

 stout cords and balls of cells (figs. 214 and 215), which have received 

 from the name of their discoverer the designation PFLUGER'S egg- tubes. 

 Occasionally these are joined to one another by means of lateral 



Fig. 215.-Section through an egg-nest of a Rabbit 



7 days old, after BALFOUR. 

 el, Ovum, the germinative vesicle (kb) of which 



exhibits a filar network ; bi, connective-tissue 



strom a ; /.z, follicular cells. 



