Ill] 



HYDRA 



51 



FIG. 17. A longitudinal section through the body of a Hydra: somewhat 

 diagrammatic, the details of the cells being omitted. Magnified. 



1. Mouth. 2. Foot. 3. Tentacle. 4. Coelenteron or digestive cavity. 

 5. Ectoderm. 6. Endoderm. 7. Mesogloea or structureless lamella. 

 8. Batteries of thread cells. 9. Testis. 10. Ovary with single ovum. 



42 



