180 



THE MECHANICAL FUNCTIONS. 



that order. But they exhibit a much greater de- 

 velopement in their organization ; having very dis- 

 tinct muscular fibres, endowed with strong powers 

 of contraction. Their digestive organs, also, as I 

 shall have afterwards occasion more fully to notice, 

 are constructed upon a more complicated plan than 

 those of the polypus. Fig. 86 exhibits an Actinia 

 in its contracted state. When their tentacula, 

 which surround the mouth, and are very numerous, 

 are fully expanded, (as shown in Fig. 87,) these 



animals present a striking analogy of form to many 

 of the composite flowers ; and accordingly the par- 

 ticular species are named from these resemblances, 

 the sea-anemone, the sea-marygold, the sea-carnation, 

 the sun-fiower, daisy, &c. The tentacula are co- 

 nical muscular tubes, perforated at their extremity 

 by a minute orifice, which the animal can close at 

 pleasure, and through which the sea-water is ad- 

 mitted into cavities in the interior of the body 

 which form a circular channel round the mouth, 

 connecting the basis of all the tentacula. They 

 may be distended simultaneously by means of water 

 injected into them from this channel. Actiniae are 

 seen in great numbers on many shores, adhering 

 by their flat surfaces to rocks, and being generally 

 permanently fixed to their abode. When the wea- 

 ther is fine, and the sea calm, it is very amusing to 

 watch the rapid expansions and retractions of their 



