2 22 Shell Life 



retains her egg capsules beneath her foot until tliey 

 are hatched. The internal plate of the shell appears 

 to serve for attaching the animal, and obviates the 

 development of a very powerful muscle such as is 

 found in the Counnon Limpet. 



The Periwinkle family (Littorinidfe) have a solid 

 spiral few-whorled shell, with a round mouth closed 

 by a horny operculum. The animal 

 has a broad extended muzzle, and awl- 

 shaped tentacles with the eyes at their 

 Single row of teeth basc. Thc undcr-sidc of the foot is 

 from the raduia jjjarkcd bv a Central line, and in elidinor 



of Periwinkle •/ ^ ^ ' . . . 



the sole on either side of this line is 

 advanced alternately. Most of the species are 

 strictly littoral in their habits, and seldom wander 

 far below extreme low - water mark ; one of our 

 native species, indeed, is only covered by the sea at 

 the periods of very high tides, and when heavy seas 

 throw their big waves far up the shore. Respira- 

 tion is effected by means of a single gill -plume, 

 which is contained in a chamber formed by the 

 mantle. Their principal food at least is of a vege- 

 table nature, for the rasping of which they are pro- 

 vided with a very long raduia. The sexes are 

 distinct ; the males smaller than the females. The 

 relative position of the organs will be seen in this 

 diagram of a partial dissection. 



The Dwarf Winkle (Littorlna ohtusata) is the 

 yellow, red, brown, purple, or green shell that is so 

 abundant on all our beaches. In the empty condition 

 it is piled up at the base of the rocks after a storm ; 

 in the living state it will be found in profusion on 

 the Bladder Wrack (Fiicits vesiculosus), where it x^ry 



