480 



not sanguine enough to think, that their denaonstration here, other 

 than by their occasional products, the embryoraas, will be at all an 

 easy task. 



The Formation of Secondary Germ-Cells. 



In his well-known memoir on the development of the ovary (1878) 

 Balfour describes a twofold mode of formation of "permanent ova'* 

 (secondary germ-cells) from "primitive ova" (primary germ-cells). The 

 one of these methods is essentially that set forth by Semper (1875), 

 the other is characterised by the formation of nests of nuclei and the 

 breaking down of cell-boundaries. The nuclei of the polynuclear mass 

 increase in size, and from delicate vesicles (? vacuoles), filled with 

 fluid. Other changes take place, for an account of which the reader 

 may be referred to the original memoir. 



On reading Balfour's description the writer was struck by the 

 similarity of these changes to those, termed by Flemming "chromato- 

 lysis". As already recorded, the degeneration of germ-cells is accom- 

 panied by "chromatolysis". 



As Balfour's figures threw no light upon the matter, an examin- 

 ation of later Scyllium-embryos was resolved upon. From this it 

 presently became clear, that in both male and female specimens of 

 Scyllium canicula, the form studied by Balfour, secondary germ- cells 

 do degenerate with chromatolysis in the testis or ovary in very late 

 phases, long after the sex is established. Balfour's description refers 

 to examples of 7 centimetres in length, the writer has witnessed the 

 degeneration of such cells in specimens of 39, 45, 60, and 70 milli- 

 metres. This degeneration was erroneously described by Balfour as 

 a second form of secondary germ-cell-formation. 



Similar degenerative phenomena have been put on record by 

 Flemming in mammals and amphibia, and by 0. Hertwig in Ascaris. 



The process may, indeed, take place at any period of the Ufe- 

 history ; for it is now known to happen in the very earliest phases of 

 the development, in young and in older embryos, and in sexually im- 

 mature and mature organisms. 



There is, therefore, in Elasmobranchs one mode, and one only, 

 of the formation of secondary germ-cells and follicles, to wit, that 

 originally described by Semper and confirmed by Balfour. 



The so-called Germinal Epithelium. 

 For nearly thirty years embryologists have believed and taught 

 the origin of germ-cells or "primitive ova" from epithelial cells of 



