THE COMMON SEA MAT. 611 



nature, for they are the submarine houses of a vast class of ani- 

 mals technically called Polyzoa, because many distinct animals 

 are associated together in one community. 



For many years their place in the scale of creation was ex- 

 tremely dubious, but they are now acknowledged to be allied to 

 the molluscs, and to be really of a higher nature than the bright 

 and active insects. In general form they so resemble the zoo- 

 phytes that the two great groups have been confused together, 

 although they are in reality farther apart than the monkey and 

 the snail. They assume various forms, which may be reduced to 

 three, namely, a flat, leaf-like shape, a form as of delicate branch- 

 ing twigs, and a flat series of cells spreading over other substances, 

 such as the stem or frond of a sea- weed, an empty shell, or sub- 

 merged plant, and similar objects. 



The most familiar of these Polyzoa 'is the common Sea Mat, 

 which has already been mentioned, and which is called by the 

 scientific name of Flustra foliacea. If the finger be passed over 

 one of these leaf-like objects, a decided roughness is felt, like the 

 surface of a file, and if it be drawn through the hand from base 

 to tip, the roughness becomes so marked that the leaf can hardly 

 pass. The reason for this roughness may be seen by reference to 

 Fig. 12, which is a magnified representation of a part of the same 

 object. It will be seen that the Flustra is composed of a vast 

 number of cells, each cell being furnished with little tooth-like 

 projections, which produce the roughness already mentioned. 



The cells are formed by their inhabitants, and very much re- 

 semble in outward form the polypi which fill the cells of the zoo- 

 phytes, each of which possesses a beautiful plume of tentacles, as 

 is seen in the uppermost cell. When the animals are at rest they 

 are withdrawn so closely into their cells that they can not be seen ; 

 but when they are hungry and desirous of feeding, they push 

 themselves out of their houses, like so many snails out of their 

 shells, expand their beautiful plumes, and await the food which is 

 brought to them by the action of the water. Under the micro- 

 scope they are lovely objects, and even when they are dead their 

 empty habitations are full of beauty. 



A detailed description of all the species which are represented 

 in the illustration would occupy too much space, even if it were 

 desirable. Suffice it to say, that they have been selected in order 

 to show the wonderful variety that exists among them, and the 

 exceeding beauty of their forms. Perhaps the most elegant forms 



