638 



FOURTH GREAT DIVISION OF THE ANIMAL KINGDOM. 



THE RADIATA (Radiated Animals, or Zoophytes). 



[Neither of these names is literally applicable, for all the animals in the division are 

 not radiated ; and the very name Zoophyte, " plant- animal," is a contradiction. In 

 England, the term Zoophyte is much more restricted than in France, but it is equally 

 inapplicable, excepting, perhaps, to those species, about which there are still disputes 

 as to whether they are animals or vegetables.] 



These animals have no mesial plane, but may be variously divided into symmetrical 

 parts, radiating from one or more axes. Their organs of motion, when they have any, 

 are moveable spines attached to the skin, or flexible papillae, capable of inflation. They 

 have no true system of circulation, and their nervous system is always obscure, and 

 sometimes cannot be traced. Some have a mouth and vent, others only one opening, 

 and others, again, appear to be nourished through pores. Some are of distinct sexes ; 

 some bisexual, and some are produced by buds or division. [Some very minute ones, 

 as Volvox, consist of a globular tunic inclosing a vast number of smaller globes, each 

 of which is also a tunic inclosing another generation.] Many grow in clusters upon 

 stalks, or Polypidoms — dwellings of pofvpi, which are sometimes leathery or horny, and 

 sometimes calcareous. [The individuals produce the polypidoms, and are connected 

 with it; and when they are alive, it is probably always covered with an epidermis.] 

 According as their organization is more or less complicated, they are divided into five 

 classes : — 



1. EcHiNODERMATA [Spiuy Skius] , have, besides these, the intestine and organs of 

 respiration, reproduction, and partial circulation, floating in a large cavity. The Ho- 

 lothurice are united to them ; because, although they have no spines on the skin, 

 the internal structure is even more complicated. 



2. Entozoa [Intestinal Worms], inhabit the viscera of other animals. They are 

 long and flattened ; have no visible organs of circulation or respiration ; and some have 

 a distinct alimentary canal, while others have not. [A species which infests the intes- 

 tines of the Eel was, for a long time, regarded as the young of that animal.] 



3. AcALEPHA [Sea Nettles], are round and radiated, with only one opening to the 

 body, and no organs of respiration or circulation. They approach the Polypi, only 

 their organic tissues are more developed. 



4. Polypi [Many Tentacula, once considered as plants] . These are gelatinous animals, 

 with a mouth and digestive organs more or less complicated. Many of them live in 

 clusters upon branched or expanded polypidoms, which made them be considered as 

 animal plants. [Individually they are minute, and some of them microscopic ; but still 

 they fabricate vast reefs of hard rock, consisting of salts of lime cemented by animal 



