io6 TOILERS IN THE SEA. 



with a higher object. They are, however, of still 

 higher interest when viewed as the homes, or 

 skeletons, of the simple organisms that inhabit them. 

 It would be hopeless to attempt to give any ade- 

 quate idea of their beauty, or variability, by descrip- 

 tion, hence we shall rest content with some general 

 remarks, as a conclusion to this chapter. 



In the majority the skeleton is a delicate latticed 

 shell, or receptacle, which encloses the central cap- 

 sule, in a minority, it consists only of isolated rigid 

 pieces, of a ring, or of a tripod. According to 

 Haeckel there are twelve principal forms which may 

 be regarded as morphological types of skeleton for- 

 mation. There are, for instance, the Asteroid or 

 star-shaped skeletons ; the beloid or spicular, which 

 consist of several disconnected portions ; the lattice 

 spheres ; the lattice ellipsoids ; the lattice disks ; the 

 larcoid lattice shells ; the cyrtoid lattice shells ; the 

 circoid skeleton, with a simple vertical ring ; the 

 plectoid, in which three or four siliceous spines 

 proceed from a common point ; the sponge-like 

 skeleton, in which a kind of wicker-work of a 

 more or less spongy structure is developed ; tubular 

 skeletons ; and conchoid skeletons of bivalved lattice 

 shells. 



The lattice structures are of extremely variable 

 form, but the specific conformation depends mainly 

 upon the radial spines. In some of these the entire 



