DYNAMICS OF REGENERATIVE PROCESSES 203 



number of Tubularian stems; one half of these pieces were put ver- 

 tically, but reversed, i.e. with the oral end a in the sand, in order to 

 suppress the formation of polyps at this end. The 

 other half of the pieces were also put vertically and 

 reversed into the same aquarium, but in such a way 

 that both cut ends a and h were surrounded by sea 

 water. These latter pieces formed polyps at the oral 

 end a after three or four days, while it took nine days 

 for them to form polyps at the other end. The 

 stems, however, whose oral ends were put into 

 the sand, where consequently the formation 

 of polyps at the oral end was suppressed, 

 formed polyps at the aboral end within 

 three or four days. 

 Hence, the suppres- 

 sion of the forma- 

 tion of the polyp ^ ^ 

 at the oral end pj^, 



accelerated , con- 

 siderably* the formation of the polyp at the aboral end. 



The next question was, How can the suppression of the polyp at the 

 oral end accelerate the formation of the polyp at the aboral end ? The 

 following experiments were intended to answer this question. 

 Pieces ah (see Fig. 42) were cut from a number of stems, 

 and each of these pieces was cut in two between c and d. If 

 all four cut ends were surrounded by sea water, polyps were 

 first formed at the oral end of each half; namely, at a and 

 d, where the polyp formation occurred simultaneously. Con- 

 siderably later the polyps were formed at the aboral ends 

 c and 6, and here also the polyp formation occurred simul- 

 taneously. It therefore appears as if the polarity in this 

 case were due to a condition of the nature of a current {e.g. 

 of liquid), by which certain substances were carried through 

 the stem in the direction from the aboral to the oral end. 

 Fig 42 "^^^ deposition of certain substances by the current at the 

 anterior end retards the formation of the polyp at the opposite 

 end. The idea that a current is the decisive variable in this case could 

 be tested in another way ; namely, by tying a Ugature around the stem 

 in the middle. If this is done, the polarity is done away with and a 

 polyp is formed simultaneously at both ends.f The same experiment 



* Loeb, he. cit., II, 1891. 



t Loeb, Pfliiger's Archiv, Vol. 102, p. 152, 1904. 



