Survey of the Animal Kingdom 287 



ECTODERM 



EPITHELIO- 



MUSCU1_AR 



CELL 



1 MXER- 

 SXI XI AL 

 CELL 



NEMAXOCYST 

 CN I OOBLAST 



MES03LOEA 



DIOESTIVE 



CELLS 



G LAND 

 CELL 



Fig. 90.- — Cross section through the body of Hydra. The central space is the 

 gastrovascular cavity (enteron). (Drawn by Titus C. Evans, from Potter: Text- 

 book of Zoology, The C. V. Mosby Co.) 



Fig. 91. — Nervous system of a coelenterate. (From Herrick: Neurological 

 Foundations of Animal Behavior, published by Henry Holt and Company.) (After 

 Max Wolf, 1904.) 



