STAR-FISH AND SEA-UKCHINS. 



257 



find that the central mouth leads by a short oeso- 

 plia<njs into a central stomach, and that tliis in turn 



i o ' 



communicates with the intestine, which terminates 

 in an orifice on the dorsal surface. Springing 

 from the intestine at its origin, there are five tubes, 

 each of wdiich divides into two, and the five pairs 

 of tubes thus formed extend into the five rays ; 



Fig. 34.— Lower suifacp of common Star-fish. 



numerous blind processes gi-ow out from these tubes, 

 and give rise to glandular structures, which pro- 

 bably perform the functions of a liver. 



When a section is made across the base of one of 

 the arms, the furrows or grooves before mentioned 

 are seen to be formed of two rows of plates con- 



