THE FACTORS THAT DETERMINE REGEN- 

 ERATION IN ANTENNULARIA. 



T. H. MORGAN. 



THE following experiments were carried out at the Naples 

 Zoological Station during June and July, 1900. As there may 

 be no opportunity in the immediate future of completing the 

 observations, I have determined to publish them as they stand, 

 in the hope that the results may stimulate some one, so situated 

 as to obtain the necessary material, to take up the questions 

 here raised and to bring them to a more satisfactory conclusion. 



Loeb's experiments on Antennularia, made in 1892, show 

 that pieces of the stem suspended in sea water always regen- 

 erate roots at the lower end and a new stem at the upper end. 

 The result was the same whether the apical or the basal end 

 of the piece was uppermost, i.e., whether the piece had a normal 

 or a reversed orientation. Similar results were obtained when 

 pieces were suspended obliquely, the high end producing 

 always the new stem and the low the new roots, etc. These 

 results are similar to certain results that have been obtained 

 in plants, although Vochting has shown conclusively in many 

 forms that the polarity of the piece is a much stronger factor 

 in determining the regeneration than is gravity. Loeb drew 

 the natural inference from his results, 77.7., that gravity deter- 

 mines the kind of regeneration that takes place at the ends of 

 the piece. Driesch, 1 who examined later the regeneration of 

 Antennularia, found that when a piece of the stem is so placed 

 "that its basal end is freely surrounded by water," a large 

 number of roots are formed from that end. If the end with 

 its roots is cut off, there is generally formed from the cut end 

 a few new roots, but also always a more or less delicate stem 

 composed of a few tubes. This stem is negatively geotropic. 



1 Driesch, H. Studien iiber das Regulationsvermogen der Organismen, I. 

 Rotix's Archiv. Bd. v, p. 383. 



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