90 ZOOPHYTES. 



FOURTH BRANCH OF THE ANIMAL KINGDOM. 

 ZO'OPHYTES OR RADIATA. 



LESSON IX. 



ZO'OPHYTES. Organization Division. 



CLASS OF INFUSO'RIA ROTATO'RIA. 



CLASS OF ENTOZO'A. Division Filia'ria Asca 'rides 



Tce'nia. 



CLASS OF INFUSO'RIA PoLyGAs'TRicA. 

 CLASS OF ECHINODER'MATA. Sea-stars. 

 CLASS OF ACALE'PHA. Medusa. 

 CLASS OF POLYPI. Coral Coral-reefs Hydra Sponges. 



Geographical Distribution of the Animal Kingdom. 



The animals placed in the fourth and last great division of the 

 animal kingdom possess an organization much less complicated 

 and consequently much less perfect than that of the creatures we 

 have studied in the preceding parts of our series. 



1. In the higher animals the body always consists of two 

 similar halves; all the external organs are arranged on each side 

 of the middle line, in pairs ; whenever there is an organ on one 

 side, a similar one is found on the opposite side, and the superior 

 and inferior surfaces of the body differ from each other. In 

 Zo'ophytes, on the contrary, this symmetry is seldom found : in 

 general, the different organs are placed around the axis or centre 

 of the body, so as to give it a radiated form. Sometimes this 

 arrangement is carried so far that the animal resembles a star 

 (Jig- 85) ; and in a great many of these creatures, the body resem- 

 bles an expanded flower (figs. 87 and 88). Many of them live 

 fixed at the bottom of the sea, and united to each other in such a 

 manner as to wear the appearance of branching shrubs, and this 

 external analogy to certain plants is so great, that for a long 

 time these animals were confounded with marine plants, and even 

 now that we know how much their structure, as well as their 

 functions, differ from those of vegetables, we cannot assign to 

 them a more appropriate name than Zoophytes (from the Greek, 

 zoon, animal, and phuton, plant) or plant-animals. 



2. In these animals the nervous system is entirely wanting, or 

 is found in an extremely rudimentary state : they have no special 



1. What are the general characters of Radiate animals ? 



2. What is the character of the nervous system in Zo'ophytes ? 



