588 T. H. Morgan. 



material (which has the same gradation as that in the hydranth 

 itself) than when acting in the reverse direction (namely, at the 

 aboral end). Therefore, the oral polyp, as a rule, develops 

 first. For its development it needs certain nutritive material. 

 This it finds either in the coenosarc or in the circulation, and uses 

 the material as it develops. In consequence the cut surface at 

 the basal end cannot get the material necessary for it to develop 

 into a hydranth, and it either remains undeveloped or produces 

 a stolon. If, however, we tie a ligature around the piece, the 

 aboral end may then make use of the substances that are present 

 in the isolated aboral part of the piece; hence there develops a 

 hydranth. Its development is usually delayed as compared with 

 that at the oral end of a piece cut off at the same level. Why does 

 this delay occur .? It can be accounted for in either of the follow- 

 ing ways. It may be assumed that even when the stem is tied 

 the oral end near the ligature often begins to form a polyp, and 

 this developing end uses up at first all of the available food 

 material, but a-s development at this end stops the stimulus of 

 the water on the aboral end makes that end active in the presence 

 of an excess of material. That the oral polyp may actually begin 

 to develop or even completely develop when the stem is tied, or 

 when one end is stuck into sand, or into vaseline, has been shown 

 by our experiments. On the other hand it is important to note 

 that the assumed gradation in the material from hydranth to 

 base must be first reversed before the aboral hydranth can 

 develop. The necessity for reversing the arrangement may in 

 itself account for the delay in the development of the aboral 

 hydranth, and for the prompter development of the oral one. 



As has been said, the hypothesis that I advocate is, in principle, 

 fundamentally different from that of the Bonnet-Sach's view, 

 more recently advocated by Goebel and by Loeb. I assume that 

 the results are not due to the movement in a definite direction of a 

 formative or even of a nutritive material that causes the develop- 

 ment of a hydranth. On the contrary, the hydranth begins to 

 develop and it then makes use of the material that comes to it. 

 If in special cases, such for instance as those where no circulation 

 is present, the using up of material causes a movement of nutritive 



