30 STRUCTURE AND PHYSIOLOGY 



CHAPTER II. 



On the Structure and Functions of the Polypes 

 abstractedly considered. 



On the continent the term Zoophyte has of late been used in 

 a very extensive sense, so as to include every animal which ex- 

 hibits a circular disposition of parts radiating from a common 

 centre, and many also in which this character is little or not at 

 all obvious. In this country the word has never been so em- 

 ployed excepting in translations from a foreign language : no 

 English writer ever thinks of calling an intestinal worm, or a 

 sea-jelly, or a star- fish, or even the infusory animalcules, a zoo- 

 phyte ; but he applies the name to no other creatures than those 

 which in their form, or most remarkable characters, recall the 

 appearance of a vegetable or its leading properties. In this 

 restricted sense I also use it in this work, or rather with a still 

 narrower circumscription, having assigned what appear to be 

 sufficient reasons for removing the corallines and sponges from 

 the category, and restoring them to the vegetable kingdom, to 

 which the earlier naturalists believed they had a rightful claim. 

 The definition of a zoophyte is thus considerably simplified, but 

 there remains sufficient variety and discrepancy in the consti- 

 tuents of the order to render that definition in some degree vague 

 and incongruous. The fact is — the classification of molluscous, 

 and radiated, and acritous animals requires to be recast : the 

 limits between them have not been determined with undisputed 

 precision, and it seems probable that there are in each class some 

 tribes which will pass from one to the other as discovery pro- 

 ceeds. It has been recently proposed* to remove a large pro- 



* Thompson's Zoological Researches and Illustrations, p. 92. 



