72 LOWER INVERTEBRATES. 



Branch III. — CCELENTERATA. 



The Coelenterata embrace the jelly-fishes ami corals, or more accurately speaking, 

 the Hydrozoa, Actinozoa, and Ctenophora. In the first and last of these divisions 

 fall most of those animals which are commonly known as the Medus£e, while the 

 Actinozoa include the true corals and their relatives. The endless variety of names 

 wliich one encounters in this group need not lead to confusion, and if considered in the 

 light of the historical development of the study, indicates those various characteristics 

 which have from time to time attracted the attention of students of these animals. 



Of general terms used to designate the group, that of Zoophytes is one of the 

 oldest. In the infancy of natural science, when superficial observations took the place 

 of more accurate anatomical studies, it is not to be wondered at that the likeness of 

 these animals to plants led to the present name. One of the first comparisons which 

 the novice makes, on seeing these animals for the first time, is that they resemble 

 closely members of the plant world, and in maturer studies we are continually meeting 

 similar resemblances of a deeper-seated nature 



The Ctelenterata include two of the large divisions of the Radiata of Cuvier, who 

 first outlined their characteristics in the masterly manner which marks all his works as 

 models of zoological research. The name Ca'lenterata dates back over a quarter of a 

 century (1847), to the profound investigations of these animals by Frey and 

 Leuekart, by whom it was first used. 



The limits of the subordinate group of Hydrozoa are in many particulars obscure, 

 and while many naturalists prefer to include in it a large group of gelatinous animals 

 called tlie " sea-lungs," comb-bearing medusfe known as Ctenopliora, others, from the 

 close likeness of their young to the larvse of the star-fishes, set these ajiart as a separate 

 group. The Hydrozoa as here considered include the Hydroidea, the Discophora, and 

 the Siphonophora, and contain by far the larger part of the true Meduste. 



The term Acalephje, common in many writings on these animals, is almost synony- 

 mous with that of Hydrozoa as here used. By many it is also made to embrace the 

 Ctenophora. The term was long ago used by Aristotle, and refers to the stinging 

 powers which many of the Medus£e have. Given by many authors a greater or by 

 others a less extension, it has been wholly abandoned by most of the leading students 

 of these animals. 



The Actinozoa or corals are marshalled under two divisions, the Actinoid, or true 

 reef builders and their allies, and the " sea-fans " and " sea-whips," which are called, 

 from more or less fanciful reasons, the Halcyonoids. 



The single anatomical feature which is common to the groups mentioned above, to 

 which, in jjoint of fact, they owe the name of Ca'lenterata, is the identity of a stomach 

 and the body cavity. In the simplest forms these cannot be distinguished from each 

 other, and in the higher genera there is but a slight differentiation of one from the 

 other. 



J. Walter Fewkes. 



