HETEROMORPHOSIS 153 



or the foot of Cerianthus is amputated, or if a piece is cut 

 out of a Cerianthus, the fragment, if not too small, and if 

 external conditions permit of it, again assumes a vertical 

 position, with its oral end directed upward and its aboral 

 end directed downward. I shall now describe these phe- 

 nomena in greater detail. 



1. If a Cerianthus is laid upon the bottom of a vessel 

 covered with sand, after a few minutes the foot of the ani- 

 mal begins to bend downward near its tip and to bore into 

 the sand. In half an hour or less (at the proper temperature 

 and with irritable animals) the entire animal has buried itself 

 vertically in the sand up to its head. It remains perma- 

 nently in this position, if other circumstances do not induce 

 it to move. 



2. A wire net, the meshes of which are so narrow that 

 the body of a Cerianthus can only with difficulty be drawn 

 through them, is supported horizontally upon a glass vessel 

 and set into the aquarium. A Cerianthus is laid upon the 

 wire net. After a few minutes the foot of the animal begins 

 to turn downward, and to bore through one of the meshes of 

 the wire net. That portion of the foot which has passed 

 through the wire net assumes an absolutely or nearly ver- 

 tical position, and remains so permanently. No change 

 occurs at the oral pole, except that the tentacles close together 

 so that they look like a brush, the handle of which is formed 

 by the remaining portion of the animal. The animal crowds 

 its body more and more through the mesh in the net, until 

 it finally attains the vertical position shown in Fig. 26. 



3. This orientation can also be reached within half an hour. 

 But while the Actinian generally remains in the sand after 

 having buried itself vertically in it, an animal upon the wire 

 screen rarely retains the orientation described longer than two 

 days ; it either works itself entirely through the wire screen, 

 or else retracts its foot to bore it through another mesh 



