142 DIVISION OF LABOR 



Groups of Animals 



Rote. — Animala may be arranged in an evolutionary series beginning with 



simple forms and ending with very complex forms, such as man. Division of labor 



in a steadily increasing degree is seen as we go from the simple to the higher forms. 



We shall try to arrange the forms given in an evolutionary series, beginning with the 



• simplest forms and working up to the most complex. 



a. Protozoa 



First would come one-celled animals, Protozoa. Name three 

 Protozoa which you have studied. 



b. Porifera 



Sponges, Porifera (containing pores). Examples : bath sponge, 

 Grantia. Simple fixed forms. Note a specimen of the bath 

 sponge. Has it a skeleton ? What is the internal structure of a 

 sponge? (See figure on page 180, Civic Biology.) 



c. Ccelenterates 



Ccelenterates (Ceelom = body cavity, enteron = food tube). 

 Examples : Hydra, sea anemone, jellyfish. There is a single 

 cavity in the body with one opening. (See figure on page 179, 

 Civic Biology.) The animals in this group are provided with sting- 

 ing cells. 



d. Segmented Worms 



Examples : sandworm, earthworm. Long jointed or segmented 

 animals with or without jointed legs. Nervous system on the 

 under side of the body. (Pages 183, 184, Civic Biology ) 



e. Echinoderms 



Examples : starfish, sea urchin. These animals have spines in 

 the skin, body organs more complicated. (Pages 184, 185, 

 Civic Biology.) 



f. Arthropods 



Having jointed body, jointed appendages, and outside skeleton. 

 Nervous system on under side^of the body. There are two great 

 groups of these animals : 



