Determination of Location of Central Zone 75 
In the pluricellular animals we can start out with the 
simple supposition that if a central zone of development 
is present, it is probably that in which the blastomeres 
multiply with unlike rapidity ; that is, it will be constituted 
by these blastomeres which multiply most rapidly. For 
this greater rapidity would in the majority of cases 
indicate a greater vitality or energy, which may be 
produced by a richer protoplasm or by any other special 
condition favoring the nutrition. And this greater 
energy would bring it about that the cells possessing it 
would win the upper hand over the others. 
“The zone,’ writes Oscar Hertwig, “where the 
smallest embryonal cells lie, which are also those which 
divide most rapidly, becomes the place of gastrular 
invagination; it becomes something like a fixed center of 
crystallization for the animal development.” ** But these 
blastomeres are those which, in the vertebrates for 
example, later constitute the medullary tube and 
afterward the spinal cord. 
As we shall see, everything seems to lead to the con- 
clusion that in animals with specialized nervous systems 
the central zone is constituted by the least differentiated | 
part of the nervous system itself; in the vertebrates : 
probably by the innermost periependymal part of the 
spinal cord. This part after completion of its activity in 
determining development would, on account of the so- 
matic function pertaining to it, likewise constitute the 
place where the infinitely manifold nervous activities of 
all the rest of the nervous system or rather of the whole 
organism are faintly re-echoed. 
As we have already said, this location of the central 
““8Oscar Hertwig: Zeit- und Streitfregen der Biologie. Heft. 2. 
Mechanik und Biologie. Jena, Fischer, 1897. P. 180. 
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