HETEROMOEPHOSIS 165 



smooth coating. If the Cerianthus is pulled out of the sand, 

 it is found to be incased in a soft tube which is smooth 

 internally and covered on the outside with fine grains of 

 sand. The animal can be drawn out of the tube without 

 injury. It seems very human that the animal should arrange 

 itself comfortably in the sand and protect itself against 

 unwelcome visitors by building a tube about itself. This 

 formation of tubes by Cerianthus appears to belong to those 

 cases to which the old phrases of "instinct" and "artistic 

 impulse of animals" might be applied. It may perhaps be 

 of interest to some of the readers to become acquainted with 

 the following simple experiments which show upon what 

 foundation anthropomorphic conceptions of life-phenomena 

 are occasionally based. 



1. If a Cerianthus is carefully drawn out of its tube and 

 laid upon a very thin layer of sand in which it cannot burrow, 

 a secretion is soon formed at the surface of those portions of 

 the body which rub against the sand. The surrounding 

 particles of sand stick to this secretion. The continued 

 movement of the animal, and the propagation of stimuli from 

 those parts of the animal which are rubbed in the sand to 

 neighboring parts of its surface, cause the secretion to be 

 poured out over the entire surface of the body of the animal. 

 The tube is then completed. It is at first very thin, but 

 becomes thicker in the course of time, as more secretion is 

 poured out in consequence of the continued friction. 

 According to these observations, therefore, the entire process 

 of "tube-building" is nothing but a process of secretion, the 

 stimulus for which is found in the friction of the surface of 

 the .body against solids. This is confirmed by the following 

 experiments. 



2. The thickness of the tube is dependent upon the 

 degree of friction. If one Cerianthus is laid upon sand, 

 while another is introduced into a carefully cleaned test- 



