HETEROMORPHOSIS 127 



grow almost perpendicularly away from their substratum. 

 If, in addition, the separate stems stand very close together, 

 as is usually the case, the contact of the polyps with each 

 other influences their orientation. This has the same effect 

 as would be brought about by causing each separate polyp 

 to grow in a narrow hollow cylinder. The individual stems 

 must thus not only grow away from the surfaces to which 

 they are attached, but they must grow away from it in 

 approximately straight lines. 



3. Daly ell has observed in Tubularia indivisa a form 

 very similar to Tubularia mesembryanthemum that the 

 polyps drop off after they have existed a certain length of 

 time, and that after a longer or shorter period new polyps 

 are formed in their places. As soon as a new polyp has 

 been formed, the stem begins to grow in length immediately 

 under it. The growth continues as long as the polyp exists ; 

 as soon as it drops off, growth ceases. 1 



I observed the same condition of growth in Tubularia 

 mesembryanthemum. The longitudinal growth of the stem 

 was continued to a region just beneath the polyp, and it 

 continued as long as the polyp existed; when the latter 

 dropped off, growth ceased; when a new polyp was formed, 

 the stem again grew in length. In the bioral polyps an 

 increase in length occurred simultaneously at both ends of 

 the stem, so that these stems reached a much greater length 

 in a shorter time than any of the normal specimens that 

 were ever brought to me by the collectors of the Zoological 

 Station in Naples. That the stem grows in length close 

 behind the polyps at both ends of the bioral animal is 

 clearly shown by the fact that the newly formed part is thin 

 and transparent, and thus can be readily distinguished from 

 the older opaque portions of the stem. Therefore in its 

 growth also the aboralpole of Tubularia behaves like the oral. 



1 Rare and Remarkable Animals of Scotland (London, 1847). 



