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.” *° 
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 
asthe off distinctly from the surrounding somatic tis- 
of some tissue whose special, “coma functions i in the 
adult individual are such as predispose it best, in the 
“Le Dantec: Traité de Biologie. P. 412. 
