2o6 BIOLOGICAL LECTURES. 



cut out, the material at one end will have been more anterior 

 in position in the original piece than the material at the other 

 end. This difference is sufficient, theoretically, to account for 

 the different results at the two ends. I do not assume that a 

 polarization is present, because we do not know enough about 

 any such principle, if it really exists at all, to make it of any 

 service. My assumption rests simply on the basis that at each 

 level the material is somewhat different from that at every other 

 level. These considerations give us a sufficient basis to build 

 up an idea of how the development of the piece may be thought 

 of as taking place. As soon as the piece has been removed and 

 its ends have closed in, it is possible to think of a rearrange- 

 ment of the molecular structure taking place throughout the 

 whole mass. Since the two ends are different, we can imag- 

 ine their differences to become greater and greater in the same 

 directions in which they differed at first. If the expression 

 is pardonable, the anterior end becomes more anterior, and the 

 posterior more posterior ; and this influence extending to the 

 intermediate regions, they too change in their respective direc- 

 tions. As a result, the material of the new piece assumes the 

 molecular arrangement characteristic of a hydra. Then the dif- 

 ferentiation begins that changes the entire piece into the new 

 individual. 



Let us not hesitate to push this view to its logical conclu- 

 sions and ask in what part of the material does this change take 

 place. Does each cell change and through simple contact with 

 its neighbors bring about a change in them, and so from cell to 

 cell ? In other words, is the result an intercellular reaction } 

 While it might be possible to look at the result as brought 

 about in this way, still, I think there are several important 

 reasons why we must regard the change as more fundamental 

 than that involving only the cells as units. I cannot take up 

 at this time my reasons for so thinking, but I may point out 

 that since in the Protozoa and in the eggs and embryos of other 

 forms changes similar to those I have described take place, we 

 seem to be forced to the conclusion that the change is in the 

 whole protoplasm and is probably a molecular change of the 

 protoplasm. 



