I2O C. M. CHILD. 



tion of the existence of inhibiting substances becomes wholly 

 unnecessary. And finally, the definite and characteristic spatial 

 relations between different axes in such a complex as the multi- 

 axial plant and the hydroid cannot be accounted for in terms of 

 the production and transportation of inhibiting or other sub- 

 stances. No sort of transportative relation can be conceived 

 which affords an adequate interpretation of the facts. Only 

 on the basis of transmission in protoplasm is it possible to account 

 for both origin and maintenance of the relations which are 

 demonstrated to be present in the organism. Of course after 

 parts have become qualitatively different, more or less specific 

 chemical relations undoubtedly exist between them, but these 

 are results of physiological integration, not its determining con- 

 ditions. Further discussion is postponed until additional evi- 

 dence along other lines is presented. 



GRADIENTS ix STAINING WITH VITAL DYES. 



When neutral red or methylene blue is used in determining 

 differences in susceptibility, it is found that while these dyes 

 enter all cells of the hydranth readily, differences in rate of stain- 

 ing appear in the earlier stages of the process. These differences 

 show the same relations to the axes and to stage of development 

 as the differences in susceptibility. The axial gradients in rate 

 of staining indicate the existence either of differences in per- 

 meability to the dyes or of differences in the rate at which they 

 are adsorbed or otherwise taken up by the cell constituents, or 

 perhaps differences of both sorts. That the dyes are held in 

 some way within the cells is evident from the fact that they 

 accumulate there until their concentration is far higher than out- 

 side and do not pass out to an appreciable degree when the ani- 

 mals are returned to water. Similar differences in rate of stain- 

 ing with vital dyes, showing in general the same regional relations 

 as the differences in susceptibility, have been noted in many other 

 forms, both plant and animal, but it is evident that in the hy- 

 droids, as elsewhere, the differences in susceptibility to the dyes, 

 as measured by time of death, cannot be due alone to the fact 

 that the dyes enter certain cells more rapidly than others. 

 Most of these differences in rate of staining, e.g., those in dif- 



