90 Cell-Pedigrees 



some groups of the animal kingdom and a little later 

 in others. 4 



In my picture, however, sexual cells are never pro- 

 duced by somatic ones, but the main lines are always 

 drawn through the ancestral rows of the germ-cells. Ac- 

 cordingly these produce all the somatic rows of cells. 

 We see that it is merely a matter of choosing the main 

 lines for the picture, and not of a comprehension of the 

 facts. But with my choice the picture becomes simple 

 and clear, and essentially the same for plants as for ani- 

 mals. To my mind the germ-cells of the hydroids and of 

 the phanerogams are not, as Weismann assumes, 5 secreted 

 by the Metazoon itself, but are formed, as in the case of 

 all other sexually differentiated heteroplastids, on the 

 germ-tracks, only the number of cell-divisions which pre- 

 cede their origin on this track is here very great. 



According to my definition, a germ-track never origi- 

 nates from a somatic track. A continuity of the germ- 

 cells does not occur as a very rare case, 6 but everywhere, 

 and without exception, although sometimes at a great 

 distance, along the germ-track. The whole question of 

 whether somatic plasm can change into germplasm 7 is, 

 on the basis of my conception, deprived of any founda- 

 tion in fact. But it certainly is not always easy to decide 

 whether a track is to be regarded as a somatic one or as 

 a germ-track, as will be seen from the next chapter. 



For a clear comprehension of the phenomena of he- 

 redity the conception of the germ-tracks, as it has been 



4 Weismann, A. Zur Frage nach der Unsterblichkeit der Einzellig- 

 en. Biolog. Centr. 4: 683. 

 5 Loc. cit. p. 685. , 



6 Weismann, A. Die Kontinuitdt des Keimplasmas. p. 11. 

 7 Loc. cit. p. 52. 



