The germ-cells. 695 



arises. Probably with the new divisions the faculty of developing 

 spontaneously becomes lost. At any rate, they have entered upon a 

 portion of a life-cycle, leading directly to a new conjugation of gametes, 

 and most certainly they have evaded the line, ending in a cul-de-sac, 

 the formation of an embryo. 



If one examine the life-cycle of the germ-cells from any con- 

 jugation to a succeeding one, leaving out of consideration the formation 

 of a larva or of an embryo, it is obvious, that in all its details it 

 resembles closely the life-cycles of many Protozoa. 



Conjugation of two unlike gametes is followed by a number of 

 cell-divisions, the products, the primary germ-cells, containing the 

 duplicated number of chromosomes. Then comes a resting phase, 

 conditioned by the environment within the developing embryo. By 

 and by, there are new divisions, still with duplicated chromosomes, 

 the products being the secondary germ-cells, and these mitoses cul- 

 minate, as in many Protozoa, in certain divisions, preceded by a 

 reduction of chromosomes, just prior to a new conjugation. 



Indeed, the germ-cells may be regarded as unicellular 

 organisms, which pass one part of their life-history 

 within a multicellular sterilised stock, the embryo, or 

 Metazoon, formed by one of them at a definite period 

 in the life-cycle. 



Necessarily, from this point of view the immortality, postulated 

 by Weismann for the Protozoa and for the germ-cells of the higher 

 animals, but denied by him to the Metazoa themselves, attaches to 

 the germ-cells, and not to the embryo. 



In this way the continuity of a hypothetical germ-plasm resolves 

 itself into an actual morphological continuity of germ-cells. 



Note. In Part II of "The Germ-cells" the germ- cells of Pristiurus, 

 as worked out in some 56 embryos and blastoderms, will be treated 

 of. In Part III it is intended to resume the account of observations 

 upon Raja hatis. 



