REGENERATION IN TUBULARIA CROCEA. 299 



III. THE REGENERATION OE SHORT PIECES OF THE 

 STEM OF TUBULARIA. 



It was first noted by Bickford (i), and later confirmed by 

 Driesch (2) and by Morgan, that small pieces of the stem of 

 Tubularia about I mm. in length are capable of regenerating. In a 

 recent paper, Hargitt (5) states that he was unable to obtain any 

 regeneration from pieces of the stem of Tubularia crocea and of 

 Tubularia teueUa that were as much as 3-4 mm. in length. This 

 result was probably due to the poor condition of the stems when 

 the experiments were made. Small pieces of the stem of some 

 other hydroids, do not appear to possess as great a power of 

 regeneration as Tubularia, for Cast and Godlewski (4) have 

 found that pieces of the stem of Pcnnaria cavolinii about i mm. 

 in length never produce hydranths and pieces 2 mm. in length 

 regenerate hydranths but rarely. Bickford's experiments on 

 small pieces of the stem of Tubularia tenella show that, in this 

 species, regenerative processes are not restricted to any special 

 region of the stem, and also that such short pieces tend to form 

 one complete hydranth rather than to produce double abnormal 

 structures. 



In experimenting on Tubularia mesembryanthemum, Driesch 



(2) found that of 82 short pieces of stem, 5 formed a single 

 proboscis, 26 formed a double proboscis, and the remaining 5 i 

 pieces produced hydranths. These results agree with those of 

 the earlier experiments of Bickford. In a later paper, Driesch 



(3) states that at the oral end of the stem one seldom gets a 

 whole hydranth, but usually a single or a double proboscis ; 

 from the middle zone hydranths usually develop ; while from the 

 aboral end of the stem, these structures are rarely produced. 

 This difference in the kind of regeneration from the various parts 

 of the stem Driesch attributes to the situation of the small piece 

 in the onVinal individual and to the different distribution of the 



O 



hydranth-forming pigment in the coenosarc of the different parts. 

 Since Morgan and also Stevens (i 1-12) have proven the fallacy 

 of the hypothesis of "red formative stuff" in Tubularia, this 

 portion of Driesch's explanation is, of course, no longer tenable. 

 Morgan (S-io) has made an extended series of experiments with 

 small pieces of the stem of both Tubularia imsembryanthemum 



