42 INTRODUCTION TO ZOOLOGY CHAP. 



The best way of getting them is to lift them out of the sea 

 beyond low tide mark in a pail of water, and then to transfer them 

 to a large tank of sea- water, or a clear rock pool, dipping the pail 

 right in, so that they gradually float out ; in this way beautiful 

 undamaged specimens of Aurelia may be obtained. 1 



2. Further examination of dead, pickled specimens l is desir- 

 able, and one should be cut in halves longitudinally to expose the 

 gastric cavity and the structures within it. 



Class III. : ANTHOZOA OR ACTINOZOA 



(SEA-ANEMONES AND CORALS) 



Type : The Sea-anemone. 



There are a great many different genera of Sea-anemones 

 common round our coasts, where they are to be seen fixed 

 to the rocks between high and low tide marks ; they vary 

 considerably in external form and in their beautiful colours, 

 but all have essentially the same general type of structure 

 and of life-history. 



External The body consists of an almost cylindrical 



Appearance column, varying in length from a fraction of an 

 and Habits. inch to 6 or 7 i ric h es ; it broadens slightly at the 

 base, and this end is attached to a rock, whilst the narrower 

 upper end consists of a flat disc with a slit-like mouth in the 

 centre, and a fringe of tentacles (usually some multiple of six 

 in number) all round the margin of the disc. 



If touched, the whole body seems to collapse, for the 

 water which filled its cavity is expelled and it immediately 

 becomes an almost shapeless mass. The tentacles are also 

 tucked away quite out of sight, for a circular muscle round 

 the top of the body contracts, and pulls together the margin 

 of the disc, like a string drawn round the mouth of a bag. 

 Both the tentacles and the body -wall are furnished with 

 many stinging cells (nematocysts), which serve to protect the 

 animal from enemies and also aid it in killing its prey, which 

 consists of worms, shrimps, and many small animal forms ; 

 these are paralysed by the nematocysts and then passed 

 through the mouth into the digestive cavity within, the 

 indigestible parts being ejected again through the mouth. 



1 These are also supplied by the Biological Laboratory, Plymouth. 



