44 BIOLOGICAL LECTURES. 



we offer them bits of meat. They endeavor to force it into 

 the new oral disc, where the mouth ought to be, but where no 

 mouth exists, and only after a struggle of some minutes give up 

 the hopeless attempt. I tried in every possible way to produce 

 tentacles in the aboral end of a piece which had been cut out, 

 but without success. 



Hydra behaves, as regards polarization, a little differently 

 from Cerianthus. If we make an incision in the stem, a 

 whole new oral pole grows out, but otherwise it, too, shows 

 polarization. 



A good many animals, so far as is yet known, reproduce 

 only the lost organ, but never show any heteromorphism. We 

 see, therefore, that while in some animals we are able to pro- 

 duce heteromorphosis, in others the most definite polarization 

 exists, and we are able to produce regeneration of lost parts 

 only in the arrangement which exists in the normal animal. 

 In this case we must assume that unknown internal conditions 

 determine the arrangement of limbs. 



In addition to examples of heteromorphosis or polarization 

 occurring separately, we find cases in which both phenomena 

 are exhibited by the same animal. If we cut out a sufficiently 

 large piece of the stem of Tubularia mesembryanthemum, and 

 place it in the bottom of a dish of water, carefully protected 

 from jarring, the anterior end of the piece gives rise to a new 

 polyp, the posterior end to a root ; but if we hang up the stem 

 in such a way that the posterior end does not touch the surface 

 of the glass, and is sufficiently provided with oxygen, this end, 

 too, produces a polyp, and we have a true case of heteromor- 

 phosis. In all cases the polyp at the oral end is formed first, 

 and a relatively long time (one or more weeks) elapses before 

 the aboral polyp is formed. But under one condition I could 

 cause the stem to form a polyp at the aboral as quickly as at 

 the oral end, namely, by inhibiting or retarding the formation 

 of the oral polyp. This could be done readily by diminishing 

 the supply of oxygen at the oral end. In such cases the 

 aboral polyps were produced nearly as quickly as the oral 

 polyps. 



