243 



SIPUNCULID^E, 



OR YERMIGRADE ECHINODERMATA. 



In the animals of which we have now to treat, Radi- 

 ism sets and Annulism appears. In their external ap- 

 pearance they are worms, for the likeness they bear to 

 the Holothurise depends on a correspondence with the ver- 

 miform, and not the radiated characters of those animals ; 

 but internally they afford evidence of belonging- to the 

 same great class. They are, in fact, Annelidous Radiata, 

 the transition between the Radiated and Symmetrical 

 types of form. They have no rows of suckers ; their bodies 

 are not divided into a quinary arrangement of lobes or seg- 

 ments ; their mouths are either not surrounded by ten- 

 tacula, or their tentacula are no longer regulated by a 

 definite number. Their motions and habits are those of 

 worms. Instead of having their skins strengthened by 

 calcareous spines, such as have prickly appendages have 

 corneous bristles, nearly resembling those seen in many 



