430 POLYPIFERA. 



Anemone (Fig. 712), which do not form associations, and which 

 deposit no hard skeleton, but which are closely allied in general 

 structure to those that do. In the classification founded only 

 upon the characters of the compound masses, therefore, the 

 naked Polypes (as they were termed) were associated in a 

 separate Order. By this method, as by any which depends 

 upon a single set of characters, and is therefore artificial, beings 

 the most dissimilar were associated together ; and those which 

 were really allied in the structure of the individuals were separ- 

 ated, because there was a dissimilarity in the form of the com- 

 pound masses. 



1120. The recent researches of Naturalists have also shown 

 that many of the creatures formerly regarded as Polypes, and be- 

 longing to an Order in which the lowest type of organisation was 

 displayed (the Order of the Hydroida), are in reality only stages 

 in the development of free-swimming Radiated animals, belong- 

 ing to the class of Acalephas of Cuvier and subsequent writers ; 

 and as it is equally unnatural to separate the young animal from 

 its parent, or to place it in a distinct class from other animals 

 closely resembling it in organisation, although not known to pro- 

 duce free Acalephs, it has been usual of late to arrange the 

 Hydroid Polypes in one class with the Jelly-fish and their allies, 

 to which, as already stated ( 1089), the name of Hydrozoa has 

 been given. The class of Polypes therefore is to be regarded 

 as including only those species which, whether simple or com- 

 pound, possess a stomachal sac separated by a certain space from 

 the general integument of the animal, and in which the texture 

 of all the soft parts of the body is firmer and less gelatinous, and 

 the whole organisation higher than in the Hydroid Polypes. 

 These true Polypes are divisible into two Orders, distinguished 

 by characters derived both from the animals themselves, and in 

 the case of the compound species from the structure of the polypi - 

 dom. The HELIANTHOIDA have the mouth surrounded by a con- 

 siderable number of tubular tentacles, and when furnished with 

 a polypidom, this is always of a stony nature, and the individual 

 Polypes are imbedded in cells excavated in its substance ; the 

 ASTEROIDA possess only eight flat, fringed tentacles ; the ani- 



