336 IN LOWER FLORIDA WILDS 



grove trees, and only occasionally descends to the 

 water to moisten itself. 



In the warmer parts of the world a great number 

 of mollusks have gone a step farther (Cyclosto- 

 midae and allies), for they have left the sea alto- 

 gether, and though they retain the operculum the 

 gill has become modified into a sort of breathing 

 sac or lung. At least four such species are found 

 within the United States, doubtless derived from 

 the American tropics. Most of our land snails 

 have become pulmonates, that is they breathe 

 by means of a simple lung, and they have not only 

 developed this from the breathing sac but have in 

 almost all cases lost the operculum. 



Many of our terrestrial snails are provided with 

 a remarkable set of calcareous "teeth" and lamel- 

 lae in the throat and aperture of the shell, and these, 

 doubtless, serve to protect the animal from attacks 

 of carnivorous beetles. In some cases this forti- 

 fication is amazingly intricate, a veritable Cretan 

 labyrinth, almost as complicated as the lock of a 

 modern burglar-proof safe, and one might suppose 

 that the animal would sometimes forget the com- 

 bination and be unable to find its way out. Occa- 

 sionally these "teeth" are crowded close together 



