62 'Indications of a Central Zone of Development 



another, it follows that at least each quarter of the 

 embryo must have its own system of correlation networks 

 independent of the other quarter systems. But the four 

 quadrants have one zone which is common to all. Con- 

 sequently at least these four independent systems of cor- 

 relation networks for the four quadrants must come off 

 from this common zone. 



This suffices to warrant the statement that this latter 

 must belong to a central zone of development, in the sense 

 which we have set forth above; and that from this zone 

 must branch off and diverge independently of one another 

 the different great correlation networks or principal 

 branches for the general distribution of nervous energy. 

 These latter divide further into progressively smaller 

 ramifications, one could almost say just as the great 

 arterial trunks coming off from the heart continually sub- 

 divide down to the terminal capillary vessels. 



It is nevertheless advisable to study these phenomena 

 more closely. We must postulate that each of the two 

 blastomeric nuclei obtained in the frog's egg after the first 

 segmentation, when it once becomes completely isolated, 

 is capable of giving rise to a complete embryo. But in 

 the experiments of Roux, the disposition of the nutritive 

 yoke or deutoplasm in the uninjured blastomere remains, 

 thanks to the retention of its place by the injured blasto- 

 mere, the same as the disposition which would have 

 existed in this same blastomere if development had pro- 

 ceeded normally. Therefore, of all the specific potential 

 energies which the uninjured blastomeric nucleus would 

 be capable of activating successively, there would com- 

 mence and continue to be activated only those which in 

 normal development would have flowed directly into the 



