28 INTRODUCTION TO ZOOLOGY. 



cilia, from which circumstance the order has been aptly termed 

 " ciliobrachiata." These cilia are " contrived a double debt 

 to pay," for they not only create currents which bring their 

 food within the reach of the Polypes, but they are organs of 

 respiration, and find in the aerated water which surrounds 

 them the means of fulfilling their appointed functions. 



To this class of Zoophytes belong the " Sea-mats;" or, to 

 use a more scientific term, the species of the genus " flustra," 

 a word derived from the Saxon, and signifying to weave. 

 Some of these encrust shells or seaweed, others present a 

 foliated appearance of a determinate pattern. They furnish 

 another example of the great abundance of animal life in some 

 of the lower tribes. Though not thicker than common letter- 

 paper, they exhibit, either on one or both" sides, successive 

 rows of cells, each of which has been occupied by its own 

 inhabitant. In one species found on the Irish coast, and with 

 cells upon one side only, Dr. Grant calculates "there are 

 more than eighteen cells in a square line, or 1,800 in a square 

 inch of surface, and the branches of an ordinary specimen 

 present about ten square inches of surface ; so that a common 

 specimen of Flustra carbasea presents more than 1 8,000 polypi, 

 396,000 tentacula, and 39,600,000 cilia." 



The spectacle presented by one of these polypidoms, when 

 in a saucer containing sea-water, and placed under the micro- 

 scope, is full of interest. Whether the animals lie in a state 

 of repose, or with the tentacula expanded and in full activity, 

 their aspect and motions are all indicative of happiness. This 

 conviction enhances the pleasure with which we regard them ; 

 for truly has the poet said, 



" The heart is hard in nature 



that is not pleased 



With sight of animals enjoying life, 



Nor feels their happiness augment his own." COWPER. 



To the scientific zoologist, it is highly instructive to con- 

 template the affinities which connect these Polypes with 

 creatures so highly organised as the Mollusca. Many similar 

 examples occur in his researches, linking together in close 

 relationship beings which are widely severed in his classifi- 

 cation, and showing that " the chain of beings" of which the 

 poet has sung has no real existence in nature. 



