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THE AMERICAN NATURALIST [Vol. XLVIII 



not always hold true, for individual L reverted toward 

 the more radial type of symmetry. From these few cases 

 it would appear that individual peculiarities tend to pre- 

 dominate over ancestral influences in the process of re- 



TABLE IV 



METRY IN THYONE 



generation. Specimens W, X, Y , are included in this 

 table to show further the correlation between Polian ves- 

 icles and retractor muscles. 



Discussion and Summary 

 There remains to be discussed the general bearing of 

 the foregoing experiments. First, the difference in the 

 number of Polian vesicles in different Thyone is partly 

 compensated by a variation in size, the fewer the number 

 the larger their size, though this ratio would not be an 

 exact one. In other words the total volume of the Polian 

 vesicles in any given specimen bears a general relation to 

 the size and functional activity of the animal. Notwith- 

 standing this functional relationship since the actual 

 number varies so widely it would be interesting to com- 

 pare the number found in other species of holothuria with 

 the conditions in Thyone. The data secured on this ques- 

 tion were meager and not very definite. For example, 

 Packard in one of the older text-books says in speaking 

 of Thyone, 



