HOLOTHUHIDA ; nOLOTHURIA. 4/3 



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

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

 usually exist. 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, 



FIG. 710. PENTACTA. 



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. 



1113. Although the body is not furnished with any complete 

 calcareous skeleton, we occasionally find a circle of plates around 

 the mouth. These afford attachment to the muscles, which 

 stretch along the entire surface of the body, and which are con- 

 cerned in its alterations of form. The mouth does not lead to a 

 distinct stomach ; but it is the commencement of a long aliment- 



