20 ZOOLOGY DIRECTIONS 



5 (4) Body radially symmetrical; body wall not pierced by 



pores. Body composed essentially of two layers of cells 

 without a cavity between them. Inner layer forms digestive 

 system. Anns wanting. Parts of the body not usually ar- 

 ranged in five or multiples of five, phylum coelen- 

 TERATA (see page 22) 



6 (3) Body usually bilaterally symmetrical, or in part spirally 



coiled, never radially symmetrical 7 



7 (15) Body not divided into segments. (In determining this 



point examine various surfaces of the body. Wings and 

 other structures frequently obscure evidences of segmenta- 

 tion on the dorsal surface) 8 



8 (11) Body usually large, not worm-like. With a skeleton 



and sometimes with jointed appendages. If skeleton and 

 appendages are both lacking, the body may be encased in a 

 limy shell 9 



9 (10) Completely or partially encased in a limy shell com- 



posed of one or two pieces. Soft parts of body inside shell 

 either bilaterally^ symmetrical or in part spirally coiled. 

 Ventral surface provided with a heavy muscular locomotor 

 organ, the foot, phylum mollusca (see page 22) 



10 (9) With an axial skeleton consisting of a skull and verte- 

 bral column. Nearly always with two pairs of jointed ap- 

 pendages. Central nervous system entirely dorsal to ali- 

 mentary canal, phylum chordata, .subphylum verte- 

 brata (see page 28) 



11 (8) Body small, worm-like, not provided with shell, skeleton 



or jointed appendages 12 



12 (13) Body flattened dorso-ventrally. Alimentary canal con- 



sisting of a pharynx and a branching intestine without any 

 anus, phylum plzVthelminthes (see page 22) 



13 (12) Body cylindrical or flattened. Alimentary canal al- 



ways terminating posterially in an anal opening 14 



