ENCRINITES. 107 



apparatus called the " water- vascular system." In 

 the sea-urchins and common star-fishes this highly de- 

 veloped hydraulic machinery is immediately applied to 

 locomotive purposes, and these creatures are thereby 

 enabled to move about over the sea-floor. In the 

 crinoids, the water-vascular system is also employed 

 for respiratory purposes. But, even in the shapes of 

 the Eckinodermata, varied though they be, we pass 

 very naturally from one type to another. Thus, 

 we might begin with living Encrinites, such as the 



Fig. 89. Body, or centre, of Euryale costosa (back view). 



Rhizocrinus of northern seas ; the rare and beautiful 

 Pentacrinus Caput-Medusce of West Indian seas, 

 nearly related to the abundant species (P. briar eus) 

 found in the Lias ; and the little Pentacrinus Europcetis, 

 occasionally dredged up in quiet spots off the southern 

 coasts of Ireland. The latter has a jointed stem, and 

 is usually attached to Sertularians. It is now known 

 to be only the larval stage of the common Feather- 



