CHAPTER II. 



POLYPIFERA. 

 ZOOPHYTES, OK POLYPS. 



Y the term Zoophytes, taken in its strictly 

 limited sense, is understood a class of 

 creatures which, in their form, or most 

 remarkable characters, recall the appear- 

 ance of a vegetable, or its leading pro- 

 perties. The most obvious character 

 common to this vast race of animals is, 

 that their mouths are surrounded by ra- 

 diating tentacula arranged somewhat like 

 the ray of a flower ; and hence the term 

 Zoophyte. So plant-like, indeed, are 

 their forms, that the ancients regarded 

 them as vegetating stones, and invented many theories to explain their 

 growth. They are usually divided into two classes, the AntJiozoa and 

 Polyzoa. The first of these is again subdivided into three orders, the 

 Hydroida, Asteroida, and Helianthoida ; the second, or Polyzoa, into 

 two orders, the Infundibulata and the Hyppocrepia. 



The mass of scattered information that the investigators of this 

 branch of natural history had published, has been collected and arranged, 

 with refreshing enthusiasm, by Dr. George Johnston, of Berwick-upon- 

 Tweed, under the title of A History of the British Zoophytes ; in which 

 work the ardent naturalist has not only combined " the whole under a 

 system more in harmony with the anatomy of the objects than has 

 hitherto been done," but enriched it by many personal researches and 

 observations on the species found in his own neighbourhood. Of 

 Polyps/' Dr. Johnston gives the following definition : "Animals aver- 

 tebrate, inarticulate, soft, irritable, and contractile, without a vascular 

 or separate respiratory or nervous system ; mouth superior, central, cir- 

 cular, edentulous, surrounded by tubular, or more commonly by filiform 



* TfoAvs, many, and irovs, a foot. 



