THE STUDY OF SHELLS, 143 



How TO STUDY SHELLS. 



A collection of different shells should be available. 

 Teachers should take the opportunity of collecting shells 

 when on a visit to the sea-shore, or supplies may be got in 

 other ways. 



The first thing to be done in the study of shells is to 

 devote some time to a general appreciative examination of 

 a collection. Drawings should be made, and in those 

 cases where the circumstances admit of it, these should be 

 coloured. 



After the general preliminary study, some questions may 

 be asked. 



What are shells ? An appeal may be made here to the 

 pupils' experience as far as it goes. They will be familiar 

 with terrestrial snails with spiral shells, perhaps with some 

 fresh water forms, e.g. in school aquarium, or with the 

 mussels, periwinkles, dogwhelks, limpet, and other common 

 molluscs of the sea-shore. The class should be guided to 

 arrive at the conclusion that shells are the hard outer 

 parts of animals, which otherwise have soft bodies. The 

 bodies of animals which possess shells such as these are 

 generally so soft that the shell is required to keep the parts 

 in position, e.g. oyster, mussel, snail, and also to protect 

 the delicate animal from attacks which otherwise would 

 certainly be made upon it. 



Shells are supporting and protecting structures, and 

 being such constitute true skeletons. It will interest 

 pupils to learn that some creatures wear their skeletons on 

 the outside of their bodies. Such a skeleton is termed an 

 Exo- skeleton. (An internal one is usually described as 

 an Endo- skeleton.) 



Here we may ask what are the names . of some enemies 

 of these soft-bodied creatures. One of the greatest 

 enemies of the terrestrial snails is the thrush, who breaks 

 the shell upon a stone. Sea birds attack shore molluscs, 

 either breaking the shell upon the rocks or swallowing it 

 whole. And there is an interesting fish which may some- 

 times be seen in fishmongers' shops exhibited as a curiosity, 



