10 . : : jefiJN& WORTH. KNOWING. 



*" * :^:.>; ; ; ; : ; - " '' 

 in that they are provided 'with* 'kings, and thereby are fitted 



to live in air instead of water. Hence all true snails are 

 terrestrial. As the snail crawls upon a cabbage-leaf, all 

 that you can see of the body is the square head bearing 

 two long and two short horns, with the muscular base ta- 

 pering behind. There is an oily skin, and on the back is 

 borne a shell containing the rest of the body, twisted up in 

 its spiral chamber. Extending along the whole under sur- 

 face of the body is the tough corrugated disk upon which 

 the animal creeps. This foot is the last part of the body to 

 be withdrawn into the shell, and to its end, in a large divi- 

 sion of pulmonate as well as marine mollusks, is attached a 

 little horny valve which just fits the aperture of the shell 

 and completely stops it up when the animal is within. This 

 is called the operculnm. The foot secretes a viscid fluid 

 which greatly facilitates exertion by lubricating the path, 

 and snails may often be traced to their hiding-places by a 

 silvery trail of dried slime. So tenacious is this exudation 

 that some species can hang in mid-air by spinning out a 

 mucous thread ; but, unlike the spider, have not the power 

 to retrace their way by reeling in the gossamer cable. TJie 

 slime also serves the naked species as a protection, birds 

 and animals disliking the sticky, disgusting fluid ; and it 

 serves others as a weapon, seeming to benumb whatever 



