462 FISTULIDA ; HOLOTHURIA. 



entitle it to rank as the typical order of the class ; since its more 

 elevated character is only obtained by its approach towards a 

 very different type of organisation. This Order, which consists 

 of the Holothuria and its allies, is known by the absence, except 

 in a few instances, of the calcareous plates and spines of the 

 Echinida and Stellerida. The skin is soft, and very distensible 

 and contractile ; so that the size and form of the body are 

 capable of great variation. The tubular feet, however, still exist. 



FIG. 608. HOLOTHURIA. 



They are sometimes arranged in distinct rows, stretching from 

 one end of the body to the other ; and sometimes scattered 

 irregularly over the surface. The general form of the body 

 varies considerably in the different species. In some it is of a 

 nearly globular shape, as in the Echinus ; not flattened at the 

 poles, however, but prolonged at these points. In others it is 

 still more lengthened, and presents slight transverse markings. 

 And in the most aberrant species, the body exhibits an almost 

 worm-like form ; being greatly prolonged, and contracted at 

 intervals into distinct articulations. Nevertheless, in all these, 

 the radiated type is evident in the conformation of the parts 

 around the mouth. This is situated at the anterior extremity of 

 the body, and is surrounded by appendages more or less ramified 

 and fringed ; so that, on looking down upon these parts only, we 

 might almost suppose them to belong to one of the Stellerida. 



