295 



CHAPTEE XVI. 



FRESH- WATER ANIMALS. 



THE GREEN HYDRA, — TRITON CRISTATUS. — A PANIC. — HABITS. — PROGS. — 

 FRESH-WATER TORTOISES. — EMYDID^. — MARINE TORTOISES. — TURTLES. 

 — HABITS OF EMYS CONCENTRICA. — TRIONYCHID^. — MUD-TORTOISES. — 

 HABITS OF MARINE TURTLES. — ALLIGATORS. 



Htdra vmiDis. 



The chapter on "Hjdroid Zoophytes" did not describe 

 this wonderful fresh-water animal, which every one may, but 

 very few ever do, procure, and examine, and experiment 

 upon. It is more than a hundred years since Trembley, at 

 the Hague, and Baker, in London, created a sensation by 

 their revelations on the nature, habits, and reproduction of 

 these little polypes, of which there are several species found 

 in our ponds and ditches, adhering to the commonest water- 

 plants. They are w^onderfully simple in form and structure, 

 consisting of a tube or sac with a prehensile disc at one 



