Location and Structure of the Central Zone 73 



centralization (annelids, arthropods), centroepigeneses of 

 the second or higher degrees would approximate grad- 

 ually more and more the simple centroepigeneses of the 

 first degree. 



"The gastrula," adds Le Dantec further, "itself a 

 morphologic unit of higher order than the cell, can itself 

 bud off other gastrulas, just as the cell can produce other 

 cells by budding. This budding may take place always in 

 the same direction and so give rise to linear associations 

 of gastrulas, as in the worms, arthropods, etc. ; or it may 

 take place in every direction and thus produce plant- 

 like associations, for example the fibroid polyps or coral 

 polyps; it may proceed radially and so give rise to the 

 echinoderms. Even the vertebrates themselves would be, 

 according to this, the result of an individualized assem- 

 blage of a linear series originally comparable with an 

 annelid worm. That is the theory of human polyzoism of 

 Durand de Gros and Edmond Perrier." 4G 



After what has been said thus far the probable loca- 

 tion of the central zone of development of the various 

 types of organisms need not be especially treated of here. 



The place in which we must suppose it to be, which 

 naturally lies in the plane of symmetry of the organism, 

 appears almost self evident from what we have said 

 above, and will become steadily clearer from what will be 

 said in continuation. It may here be remarked merely 

 that this zone cannot be imagined as any special tissue 

 marked off distinctly from the surrounding somatic tis- 

 sues ; but must rather be a simple, indistinguishable part 

 of some tissue whose special, somatic functions in the 

 adult individual are such as predispose it best, in the 



40 Le Dantec : Traite de Biologic. P. 412. 



