flEXERA TI YE ORGA 



615 



by some of the indifferent epithelial cells. Here they increase in 

 number, and give rise to masses of variable form, composed partly 

 of true germinal cells, and partly of smaller cells with deeply staining 

 nuclei, which are, I believe, derived from the germinal epithelium. 



FIG. 411. TRANSVERSE SECTION THROUGH THE OVARY OF A YOUNG EMBRYO OF 

 SCYLLIUM CANICULA, TO SHEW THE PRIMITIVE GERMINAL CELLS (po) LYING IN THE 

 GERMINAL EPITHELIUM ON THE OUTER SIDE OF THE OVARIAN RIDGE. 



These masses naxt break up into ampulla*, mainly formed of 

 germinal cells, and each provided with a central lumen ; and these 

 ampullae attach themselves to tubes derived from the smaller cells, 

 which are in their turn continuous with the testicular network. The 

 spermatozoa are developed from the cells forming the walls of the 

 primitive ampullae ; but the process of their formation does not con- 

 cern us in this chapter. 



In the Reptilia Braim has traced the passage of the primitive 

 germinal cells into the testicular tubes, and I am able to confirm his 

 observations on this point: he has not however traced their further 

 history. 



In Mammalia the evidence of the origin of the spermatospores 

 from the germinal epithelium is not quite complete, but there can be 

 but little doubt of its occurrence 1 . 



In Amphioxus Langerhans has shewn that the ova and sperma- 

 tozoa are derived from similar germinal cells, which may be com- 

 pared to the germinal epithelium of the Vertebrata. These cells are 

 however segmentally arranged as separate masses (vide Vol. i. 

 p. 43). 



BIBLIOGRAPHY. 



(554) G. Balbiani. Lerons s. la generation den Vertebres. Paris, 1879. 



(555) F. M. Balfour. "On the structure and development of the Vertebrate 

 ovary." Quart. J. of Micr. Science, Vol. xvm. 



1 An entirely different view of the origin of the sperm cells has been adopted by 

 Balbiani, for which the reader is referred to his Memoir (No. 554). 



