CHAPTER IX. 
ECHINODERMATA, 
‘Ultra magis pisces et Echinos aquora celent.”—Hor. Z. 
In their “Natural History of the Echinodermata,” Messrs. Hupé 
and Dujardin divide this vast natural group into five orders or families, 
namely: 1, Crinoidee, stone lilies, calcareous, stem composed of 
movable pieces; 2, Asteroidee, which includes the true star-fishes ; 
3, Ophiuridee, having the disc much depressed, the rays simple, 
sometimes much divided ; 4, Echinide, comprehending the animals 
known as sea-eggs, or sea-urchins, distinguished by their rounded 
form and absence of arms; 5, Holothuroidee, with soft lengthened 
cylindrical body, covered with scattered suckers. 
The Echinodermata (from the Greek words éxives, rough, and 
3¢pua, skin, indicating an animal bristling with spines like the 
hedge-hog) are animals sometimes free, sometimes attached by a 
stem, flexible or otherwise, and radiating, that is presenting an 
appearance more or less regular in all its parts, after the manner‘of a 
circle or star, its form being globular, egg-shaped, cylindrical, or like 
a pentagonal plate; or lastly, like a star, with more or less elongated 
arms, which secrete either in all their tissues or only in the in- 
tegument, very numerous symmetrical calcareous plates of solid matter, 
sometimes forming an internal skeleton or regular shell covered with 
a more or less consistent skin, often pierced with holes, from which 
the feet issue; they are frequently furnished with appendages of 
yarious kinds, such as spines, scales, &c. 
The organisation of the Echinodermata is among the most perfect 
of all the annulose animals, serving as a transition between them and 
animals of more complicated frame. They have a digestive and 
vascular system, and a muscular system is almost always present; they 
have also either internal or external respiratory organs, and a rudi- 
mentary nervous system has been detected in many of the species. 
The nutritive system is very simple, presenting in some families a 
