ECH1NODE11MATA. 

 Fig. 64. 



149 



the tubular foot, and the vesicle appended to it, are endowed with 

 a power of independent action, so that, if the vesicle contracts, the 

 fluid within it is forced into the external tubular portion of the 

 organ, which thus becomes distended and rendered erect ; but if, on 

 the other hand, the muscular tube shrinks in turn, the contained 

 fluid is forced back again into the internal vesicle, and the whole 

 foot collapses. The arrangement referred to will be easily intel- 

 ligible on reference to the rough diagram in the next page, which 

 represents a longitudinal section of one of the rays of the Asterias 

 depicted above. The internal vesicles (Jig. 65, 1, h) occupy the 

 floor of each segment of the body, and, when viewed from above, 

 (Jig. 67, d,) the entire series resembles strings of transparent 

 beads placed above the rows of ambulacral apertures, through which 

 they communicate with the tubular feet (fig- 65, 1, g). In fig. 

 65, 2, three of these organs are represented in different states of 



