STRUCTURE OF ECHINODERMATA. 127 
Egg); and they are also arranged in rows on the surface of the 
body of the Holothuria, as seen in fig. 67. 
119. The radiated arrangement is very evident in the 
whole bodies of the Star-Fish (fig. 65), and Echinus or Sea- 
Urchin (fig. 69); but in the Holothuria (fig. 67) it is nearly 
confined to the parts about the mouth; which, however, 
exhibit it so completely, that such an animal cannot be mis¬ 
taken for one of the Articulated series, even though, as some¬ 
times happens, the body is prolonged into a worm-like 
form. The digestive apparatus in this class has usually a 
high degree of complexity, as will be seen by the accompany¬ 
ing figure (fig. 69), which shows the interior of an Echinus , 
whose globular shell has been sawn across its equator, so as 
