S66. T. H. Morgan and N. M. Stevens. 



in the regeneration of a piece cut from the stem of a Tubularian 

 is based on the condition that the circulation favors the motion 

 of various substances in the direction from the aboral to the oral 

 pole." There is, so far as we can see, nothing in the experiments 

 that establishes this conclusion, and facts already known seem 

 to controvert it. 



Sixth. After giving an approximately correct account of the 

 complete, i. e., the circular, course of the circulation (p. i6o), 

 Loeb states, "It is now generally found that only those pieces 

 form a new polyp which possess a circulation." Since the cir- 

 culation takes place in all living pieces of all sizes, this statement 

 can have, so far as we can see, no bearing on the problem. The 

 further statement "that the collection of pigment granules at one 

 cut end precedes polyp formation" gives an erroneous impression 

 and reverses the real order of events. The statement "that the 

 regeneration of a polyp proceeds from those points where the 

 pigment granules collect is unproved and we believe incorrect. 

 Whether, as stated, stems rich in pigment always form polyps 

 sooner than those poorer in pigment is questionable. It is not 

 improbable that a stem lacking in the usual amount of pigment 

 is not in a vigorous condition, hence the slower development of 

 the polyp. Furthermore, the oral end of the stem is usually less 

 pigmented than the more aboral parts, yet pieces cut from the 

 oral end of a stem produce hydranths sooner than pieces nearer 

 the basal end. 



We conclude from an examination of Loeb's argument that the 

 evidence is wanting to show that the polarity in Tubularia is "to 

 be referred to a process which is comparable as to its variety with 

 a process of streaming in the direction of the aboral to the oral 

 pole." Whether the formation of a polyp involves the using up 

 of available substances in the stem which may involve a conse- 

 quent diffusion of material toward the place where it is being 

 utilized (because there is in consequence a smaller quantity of 

 it there) will be discussed in our general conclusions; but this 

 idea is fundamentally the reverse of« the one maintained by 

 Bonnet, Sachs and Goebel, viz: that the movement of the 

 circulating fluid in a given direction determines where the 



