/. MAIN SUBDIVISIONS OF ANIMALS. 3 



is well to employ subdivisions, which may be called Sub-Types, and 

 which will separate a Type into two or three distinct groups. Such 

 divisions maybe conveniently used in the case of the Ccelenterata, where 

 the polyps and medusae, the Ctenophores and the sponges all represent 

 the Coelenterate plan of structure, yet are radically different from one 

 another, and in the Ariiculata, where the Annelids with their jointless 

 appendages, the parapodia, may be separated from the Arthropods, 

 which possess jointed limbs, the meropodia. 



A summary of the above relations may be expressed by the follow- 

 ing table, in which are expressed the grouping and subdivision of the 

 Types : 



I. PROTOZOA. 



Type I. Protozoa. 



II. METAZOA. 



A. CCELENTERATA. 



Type II. Ccelenterata. 

 Sub-type I. Cnidaria. 

 Sub-type II. Ctenophora. 

 Sub-type III. Porifera.* 



B. CCELOMATA. 



i) Zygoneura. 



Type III. Vermes. 

 Type IV. MoLLUSCA. 

 Type V. Articulata. 



Sub-type I. Annelida. 



Sub-type II. Arthropoda. 



2) Ambtilacralia. 



Type VI. Echinodermata. 



3) Chordata. 



Type VII. Prevertebrata. 

 Type VIII. Vertebrata. 



* According to the more usual arrangement of the three Sub-Types of the 

 Ccelenterata the Porifera are placed first on the ground of the semi-independ- 

 ence of the cells and the consequent resemblance to a colony of Protozoa. In other 

 respects, however, the Porifera are much modified and in their architecture and 

 skeletal structure they are more complex than are the two other Sub-Types. 



