94 The Individual Tracks 



germ-track at the first divisions, and this forms thereafter, 

 only the somatic tracks lying in the sexual glands. To 

 the Diptera must be added the Daphnoidae and Sagitta, 

 for the whole body of which, with the exception of the 

 organs of reproduction, the initial cells are also split off 

 very early from the germ-track, and by means of a rela- 

 tively small number of cell-divisions. In the vertebrates 

 the germ-track probably goes through hundreds of suc- 

 cessive cell-divisions, for the purpose of body-formation, 

 before it begins the development of the sexual organs. 



Leaving the sexual organs out of our consideration, we 

 find that the somatic tracks composing the body arise 

 from the germ-track, in the Diptera as a single twig, in 

 the Daphnoidae and Sagitta as a small number of 

 them, in the vertebrates, however, as very numerous 

 twigs. But all the tracks for the body are always formed 

 before the germ-track begins to split into equivalent 

 branches in the region of the sexual organs. 



Here lies the difference between the higher animals 

 and the plants. For in the latter the germ-track splits 

 at a very early period, and the majority of the somatic 

 tracks do not originate in the main-stem of the germ- 

 track, but chiefly in its branches. The picture of the pedi- 

 gree of the germ-cells coincides here with the picture of 

 the much ramified organism itself; it does not require a 

 detailed description. The colony-forming polyps present 

 a similar case. 



The difference becomes clearest on introducing into 

 the picture only the germ-tracks, and leaving out the so- 

 matic tracks. The cell-pedigree of a higher animal stands, 

 then, as a straight tree, ramifying only a little at its top, 

 while that of the higher plants is so richly and repeatedly 

 branching from its very origin that the branches fre- 



