202 DYNAMICS OF LIVING MATTER 



regeneration). Since then heteromorphoses have been obtained in a 

 number of animals. 



Tubularia mesembryanthemum of the Mediterranean and Tubu- 

 laria crocea of the Pacific Ocean are hydroids which consist of an un- 

 divided stem (ss, Fig. 39) from 2 to 6 cm. long, which 

 has a polyp (p, Fig. 39) at the oral, a stolon or foot w at 

 the aboral end. If a piece ab (Fig. 40) is cut from the 

 stem of a Tubularian, according to the observations of 

 Allman, a polyp forms at the oral end a, a stolon at the 

 aboral end b. Allman therefore called this animal "polar- 

 ized," thereby signifying that each element of the stem of 

 the animal possesses a different oral and aboral side. I 

 undertook to bring about a heteromorphosis in this .animal, 

 and succeeded in finding a method by which without fail at 

 j/^ the aboral cut end b of a piece of the stem a polyp can be 

 jf V" produced. This method consisted in putting the piece ab 

 with its oral end a into the sand, while the aboral end b 

 was surrounded by water on all sides. In this case a polyp 

 instead of a stolon was invariably formed at the aboral end b. The 

 oral end which is in the sand does not regenerate, presumably on 

 account of the lack of oxygen. When both ends of a piece 

 ab cut from the stem of a Tubularian are surrounded by sea 

 water, the oral end a invariably forms a polyp. The aboral 

 end b may form a stolon or a polyp. In Tubularia crocea 

 I observed that under such conditions the aboral ends form 

 polyps in about 90 per cent of the cases, and stolons in 

 about 10 per cent. In this case 90 per cent of animals 

 were obtained with a head at either end (see Fig. 41). 



There was, however, a marked difference in the velocity 

 of regeneration of the two polyps. The polyp at the oral 

 end forms without exception more quickly than the polyp 

 at the aboral end. The difference in time may vary from 

 two days to two weeks; the difference apparently being less 

 at a high than at a low temperature. Even if the piece of 

 the stem forms a head at either end an intimation of the old polarity 

 still exists, inasmuch as the oral pole is formed earlier than the aboral 

 pole.* 



In the following year I was able to show that the formation of the 

 polyp at the aboral end could be accelerated by suppressing the forma- 

 tion of the polyp at the oral end. The mode of procedure of demon- 

 strating this fact was as follows : Pieces ab (Fig. 40) were cut from a 



* Loeb, loc. cit., 1890. 



-O, 



