CHAPTER XXXIV. 



PROTOZOA, CCELENTERATA, ECHINODERMATA AND VERMES. 



ANIMALS may be separated into nine groups or divisions, as 

 follows, beginning with the lowest: 



(1) PROTOZOA. These are animals of minute size composed of 

 a nearly structureless substance called sarcode, having no cellular 

 organs, and usually asexual reproduction. 



(2) CCELENTERATA. The coelenterata are radiate animals, on 

 the plan of two, four or six, having a central body cavity com- 

 mon to digestion and circulation. 



(3) ECHINODERMATA. The echinodermata are radiating ani- 

 mals generally on the plan of five, with a calcareous dermal 

 skeleton or shell, often armed with spines, and having alimentary, 

 circulatory and nervous systems. 



(4) VERMES. The vermes or worms are bilateral animals, 

 without limbs, and with paired excretory canals, sometimes called 

 the water vascular system. 



(5) ARTHROPODA. The arthropoda are bilateral animals with 

 the body divided into segments, which carry jointed appendages 

 or limbs, and they have a well-developed nervous system, as in- 

 sects, spiders, crawfish, etc. 



(6) MOLLUSCA. The mollusca are bilateral animals with a 

 soft unsegmented body inclosed in a single or bivalve shell, as the 

 oyster and mussel. 



(7) MOLLUSCOIDEA. The molluscoidea are bilateral unseg- 

 mented animals with a ciliated circlet of tentacles. They usually 

 have a hard shell case and one or two nervous ganglia. 



(8) TUNICATA. These are bilateral, unsegmented animals with 

 barrel-shaped bodies, having a simple nervous ganglion with a 

 heart and gills. 



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