162 STUDIES IN GENEEAL PHYSIOLOGY 



tacles and meat; just as a moth must react to a flame with 

 progressive heliotropic movements, even though it after- 

 ward derives no actual benefit, but actual harm, from this 

 sort of reaction. 



4. Cerianthus remains permanently in one place if its body 

 is in contact with solid bodies and if it is properly fed. If 

 the feeding is interrupted, it occasionally leaves its tubes in 

 the sand to burrow anew after some time in some other part 

 of the sand. If, however, the head of the Cerianthus is 

 amputated, this otherwise sessile animal becomes a complete 

 noniad. It burrows, remains for a few hours in its tube, 

 crawls out again, buries itself anew in some other place in 

 the sand, only to leave its new home after a short time, etc. 

 When the tentacles have again grown, the animal becomes 

 more sessile again. 



XIII. THE IMPORTANCE OF TURGOR FOR THE GROWTH OF 

 THE TENTACLES IN CERIANTHUS 



1. Although the analysis of the mechanical conditions 

 which influence the growth of plants has made great strides, a 

 physiology of animal growth does not exist even by name in 

 the modern text-books of animal physiology. It may there- 

 fore be permissible to describe here a very simple experi- 

 ment which shows that one of the fundamental conditions 

 necessary for the growth of vegetable tissues turgor 

 must be fulfilled in animal tissues also in order that growth 

 may occur. 



It may be known to the reader that the growth of plants 

 decreases or entirely stops when they wilt, but that it in- 

 creases when a plentiful supply of water is at hand. It is 

 believed that the cell contents of the growing part of a 

 plant take up water energetically from their surroundings 

 (due to the salts of the organic acids contained in them). 

 In consequence of this absorption of water, the cell-walls 



