ORGANIZATION AND GROWTH 



241 



through. I inserted into the tube a Tubularian from which I 

 had previously cut off the root and polyp, so that the one 

 end I) was in the tube and the other end c was freely sur- 

 rounded by water in the aquarium. A polyp was formed 

 nearly always upon the free end c, but only exceptionally 

 upon the end b in the tube. The oxygen dis- 

 solved in the water within the glass tube did 

 not suffice to render regeneration possible at 

 the end b. 



That regeneration only was inhibited, while 

 the power of regeneration was preserved, is 

 evidenced by the fact that if, after not too 

 long a time, I brought the end b back into 

 fresh sea-water, regeneration occurred. 



This also explains some of the facts mentioned 

 in paper iv (Part I, pp. 123 and 124). I 

 mentioned that when one end of a Tubularian 

 is fixed in the sand, or in a narrow cleft between 

 two slides, no regeneration occurs at this end 

 (even though death does not occur at least for some time). 

 At that time I was inclined to attribute the result to mechan- 

 ical factors (pressure), but I believe now that we were prob- 

 ably dealing with lack of oxygen. 



When I suspended Tubularia3 in the aquarium in such a 

 way that the one end was very close to the surface of the 

 sand, but did not touch it, and arranged my apparatus so 

 that only a small current of water entered the surface of the 

 aquarium, and kept the whole free from movement, no 

 regeneration followed at this end. The cause for this is as 

 above. According to Jacobscn, the layer of water just above 

 the mud bottom of the ocean is poor in oxygen. 1 



It may be that a movement of protoplasm toward the end 

 of a stem is possible only when this cut end is contained in 



i JACOHSKN. Annalen der < ln-mic un<l I'harmazic, Vol. CLXVII (1873). 



'Sand 



FIG. 61 



