206 DYNAMICS OF LIVING MATTER 



is not perforated. Very soon, however, after the ligaturing, a 

 perforation at the septum on either side of the ligature occurs, and 

 the circulation is again established. One might think that the current 

 just described was responsible for the phenomena of polarity in Tubu- 

 larians, inasmuch as this current carried away certain material from 

 the aboral pole. The direct observation supports this idea to some 

 extent. As I pointed out fifteen years ago, the place where a new polyp 

 will be formed is always recognizable some time before the actual regen- 

 eration occurs, by the collecting of the red or yellow pigment granules 

 in greater density at that spot. It agrees with this statement that if a 

 piece be cut out from the stem of a Tubularian and suspended in sea 

 water, the red pigment always collects first in great masses at the oral 

 end, where the polyp is formed first, and only later at the other end. In 

 my earlier writings on heteromorphosis I pointed out that this seems to 

 be in harmony with Sachs's idea, inasmuch as it indicates a migration 

 and collection of definite substances at the end of a regenerating piece as 

 the cause of the formation of a new organ. Morgan and Miss Stevens 

 raised the objection that after the formation of the polyp the rem- 

 nants of these red granules are thrown out by the polyp. This seems 

 to me in no way to speak against the possibility that the red granules 

 contribute some substances necessary to the formation of the polyp. As 

 is well known, the red blood corpuscles perish regularly in the body, 

 and their products of decomposition form constituents of the bile. Yet 

 nobody would think of using this fact as an argument against the 

 importance of the red blood corpuscles or the bile. I am inclined to be- 

 lieve that Morgan and Miss Stevens underestimate the fact which Sachs 

 tried to emphasize, that chemical processes underlie the phenomena of 

 regeneration. 



But I am far from believing that the circulation current is the only 

 factor in the transport of substances through the Tubularian. It is 

 possible that in Tubularia we are dealing also with a current of sap 

 through specific tissue, as is found in plants. Setchell has made it 

 probable that in Laminaria regeneration always starts from that tissue 

 which conducts the nutritive material. It may be that there exists a flow 

 of material from cell to cell in the entoderm or ectoderm of the Tubu- 

 laria or both, and that this flow occurs naturally from the aboral to the 

 oral end, but that it is reversed in the aboral piece of the stem when 

 a ligature is made in the stem. Even if the fact that the pigment gran- 

 ules are carried away from the rest of the stem and are gathered 

 at the oral end be responsible for the polarity, it remains to be ex- 

 plained what keeps the granules rather at that than at the opposite end. 

 These details still have to be worked out, but I believe that we may 



