1846.] Structure and Classification of Zoophytes. 263 



shrubbery. Some of the largest and most conspicuous corals, the 

 madrepores, are limited to the temperature of 68° F. This, how- 

 ever, is the winter temperature; it is what they can endure, and not 

 that in which they can germinate. The warmest parts of the 

 Pacific varies from 80 to 85°, and it is here that madrepores and 

 brain corals luxuriate. The depth of these coral reefs is singu- 

 larly small. Twenty fathoms will include very nearly all the 

 species of the madrepore and astrsea tribes. Temperature has but 

 little influence in determining this limit, as 68° F. will not be 

 found under the equator short of a depth of one hundred fathoms. 

 Light and pressure are the principal causes which bring about 

 this result. Pressure affects the function of respiration; the waves 

 which are essential to the due performance of it do not reach to a 

 greater depth than fifteen or twenty fathoms. 



Classification. — Zoophytes constitute an order of the sub- 

 kingdom termed, 



Radiata. — Mr. Dana's views in regard to the relation which 

 these hold to other animals, may be understood by the following 

 diagram: 



I. Vertebrata. 



III. Articulata. 



Insecta, Myriapoda, 



Arachnida, 



II. MOLLUSCA. 



Cephalopoda, Pteropoda, 

 Gastropoda, Conchifera, 



Crustacea, Annelida, I | Tunicata. 



I ^^^ \ IV. Radiata. I 



I \^ ; Echinodermata, ', 



Rotifera, Entozoa, Zoophyta, Acalephae, Bryozoa. 



V. Protozoa or Infusoria. 

 " One of the results of the study of the animal kingdom," says 

 Mr. D., " has been to bring to light lines or general systems of 

 development branching up from the lowest infusoria to the higher 

 grades of life. It is not true that the forms among the lower 

 grades are actually copied in any of the imperfectly developed 

 young of the superior ; yet there is some general analogy, suffi- 

 cient to indicate that the former commence on the same system of 

 development with some of the latter, although carried essentially 



