86 MARIAN L. SHOREY 



the description of the experiments it is evident that this is due 

 to the fact that part of all the ooplasmic substances are still left 

 in the first case, while in the second, all of some of these are re- 

 moved. In the right or left half, therefore, all the metabolic 

 processes characteristic of the complete organism ma,y go on, 

 with the possibility of all the normal inter-reactions, while in the 

 anterior or posterior half some of these are omitted. 



In the development of the form of any animal, the location of 

 different materials must play an important part, but in the dif- 

 ferentiation of any particular kind of tissue the presence, some- 

 where within it, of each material normally found, is, I believe, 

 much more important. To put it in another way, an ovum with, 

 for example, six kinds of ooplasmic substances may be compared 

 to six beakers with permeable walls each containing one or more 

 chemical compounds, and all immersed in the same pan of water. 

 If beaker 1 is placed next to beaker 6, the sum total of the final 

 products will be likely to vary, at least in quantity, from those 

 that would have been obtained if it had been placed next to beaker 

 2. But if the products or the reactions going on in beaker 1 have 

 any chemical affinity for the substances in beaker 2 these will 

 doubtless, eventually be affected thereby. 



It is because of this that the transplantation of embryonic tis- 

 sue to abnormal positions in the body may prove nothing con- 

 cerning the question of correlative or self-differentiation. As I 

 have tried to show in a previous paper,^ the development of nerve 

 fibres and muscle tissue from a portion of the medullary canal 

 transplanted with somites attached may be due to the presence 

 in the circulating medium of this region of some substance found 

 in its normal location. And I know of no experiment in which 

 the wholly normal differentiation of any tissue has occurred, in 

 which this possibility, absolutely essential for demonstrating 

 self-differentiation, has been eliminated. 



But aside from the fact that experimental evidence has failed 

 to establish that some stimulus outside the tissue itself may not 



^ Shorey, M. L.,'09. The Effect of the Destruction of Peripheral Areas on the 

 Differentiation of Neuroblasts. Jour. Exp. Zool., vol. 7. 



