420 



MOLLUSCOIDEA. 



found attached to the wall of the chamber, the upper (o) yielding eggs, while 

 within the lower (t) the male elements develop. Moss-animals are therefore her- 

 maphrodite, the fertilisation of the eggs being effected by the two elements ming- 

 ling freely together in the body-fluid. In all 

 essential points, the above description would 

 apply to any one of the seventeen hundred 

 species, fossil and extant, which are known. 

 Among the larger colonies may be 

 mentioned certain fresh- water genera, found 

 attached to the roots and branches of 

 water-plants, which may form considerable 

 masses ; but these stocks are dull in colour 

 and very inconspicuous, the beauty of the 

 minute individual animals themselves being 

 invisible to the naked eye. Some fairly- 

 sized forms occur also among the marine 

 genera, which are often marked by the 

 great variety and beauty of their stocks. 

 Many of these are delicate branching or 

 tree -like growths some inches in height; 

 take, for instance, the sea-mats (Flustra), 

 or again, the still larger and more beautiful 

 lace-corals, Neptune's sleeves, such as are 

 shown on p. 421, which, in spite of their 

 name, are not true corals but bryozoans. 

 The figured lace-coral (Retepora) is found 

 in the nets used on the shores of the Atlantic 

 Ocean and Mediterranean Sea. When 

 fresh, the stocks which resemble a fine, 

 cup-shaped, or folded and frilled piece of 

 lace seem to be covered by a reddish 

 organic mass, out of which arise the delicate 

 tentacular crowns of the individual animals. 

 These are, however, too small to be seen, 

 except with a magnifying glass. When the 

 soft -parts are removed, the stock is of 

 dazzling whiteness, consisting chiefly of the chalky substance which binds the 

 separate individuals together into a colony. Between the open meshes of the 

 lace-work, multitudes of minute apertures are to be seen, which are the openings 

 of the individual chambers or cells containing the bodies of the animals, and 

 into which they can withdraw their tentacular crown as above explained. Another 

 lace -coral from the Mediterranean is shown on p. 422. It rests upon a branched 

 structure, a common calcareous alga which grows on a stone. The individuals of 

 this genus (Lepralia) are arranged in rows, and are further distinguished from 

 Retepora and other moss-animals by the fact that the animals occur only on one 

 side of the stock. We mention these lace-corals because of their being- com- 



SECTION OF AN INDIVIDUAL OF 



(highly magnified). 



