^.\ 



DIFFERENTIAL INHIBITION IN OBELIA 481 



3, and 4). The stream of cells and debris can also be observed 

 directly under the microscope while resorption is going on in 

 the living organism. 



The questions remain, how and under what conditions do 

 the resorbed elements start the migration, and where do they 

 eventually get to ? 



Text-fig. 2. 



Campanularia. End of stage 2. The hypostome has disappeared, 

 the tentacles are represented only by minute knobs, some almost 

 resorbed. Nematocysts here and there project from the surface of 

 the tentacles, one discharged. (Camera lucida.) 



We will first study a tentacle. In the normal zooid the 

 tentacle is almost twice as long as the hypostome, and its axis 

 of endoderm is composed of large cells with very definite walls 

 and flattened like a pile of discs. The endodermal axis occupies 

 more than three-quarters of the diameter of the tentacle 

 (PL 26, fig. 6). 



In the first stage of resorption the tentacle has shrunk con- 

 siderably both in length and diameter (PI. 26, fig. 7). The endo- 



