CHAPTER II 

 SPECIAL CONSIDERATION OF THE INDIVIDUAL TRACKS 



5. The Primary Germ-Tracks 

 I designate as primary germ-tracks those sequences 

 of generations of cells which, in the normal course of 

 development of the organism, lead from the fertilized 

 egg-cell to the new germ-cells (egg-cells, spermatozoa, 

 pollen-grains). They will form the subject of the first 

 paragraphs. The secondary germ-tracks, leading through 

 adventitious buds, will be considered in the subsequent 

 paragraphs. 



The primary germ-tracks, then, form the common, 

 or at least the shortest of the common, paths from one to 

 the next following generation of egg-cells. They are 

 never completely unbranched, because the normal multi- 

 plication of the species is incumbent on their ramification. 

 They probably always give off somatic twigs along their 

 entire length. But the manner and means of their ram- 

 ification, the number, position, and relative significance 

 of the individual somatic tracks, is subject to much modi- 

 fication. 



Among extreme cases may be counted one one side 

 the well known instance of the Diptera, on the other hand 

 the Vertebrates, and, contrasted with both, the higher 

 plants and the corals. In the Diptera some of the first 

 cells that usually form from the egg develop into the sex- 

 ual glands of the body. Thus the initial cells for prac- 

 tically the entire body are directly separated from the 



