MARINE ZOOLOGY OF ARRAN. 26 7 



gant movements of this star-fish, the creature must be seen 

 and watched in a vivarium, where it will voluntarily fix itself 

 to the sea-weed or to a piece of rock, and, by graceful undula- 

 tions of its arms, will be certain to command admiration. 

 The picture will be greatly enhanced if several individuals of 

 various colours orange, purple, crimson ai - e introduced 

 and judiciously dispersed. 



115. Before we leave this division of the subject, it will 

 suffice to make brief mention of the well-knowu sea hedge- 

 hog, Echinus sphcera, common in most parts of the Clyde, and 

 of which fine specimens are found clinging to the rocks on 

 Holy Island, and at Clachland Point. This curious creature 

 should be carefully examined by the young student of marine 

 zoology. It is allied to the star-fishes ; for, although spherical 

 in form, the radiated structure is readily perceived. In 

 shoi-t, it is a star-fish, with the spaces between its rays filled 

 up by plates of carbonate of lime the rays themselves con- 

 sisting of the same material the whole exterior being bent 

 over into a hollow ball, and armed, hedgehog-like, or like the 

 star-fish Uraster glacialis, with numerous sharp spines. The 

 viscera, or digestive organs, of the Echinus are contained 

 within the ball ; and its mouth is provided with a beautiful 

 piece of mechanism, worthy of examination, and designed for 

 crushing the shells of molluscous and crustaceous animals on 

 which it feeds. Its mode of progression, by means of its 

 spines and suckers, is both interesting and wonderful. Speci- 

 mens are frequently found of the richest crimson or purple. 

 Another species of this genus, Echinus miliaris, is also common 

 in the pools. It is more diminutive than the former. The 

 dredge will generally be needed to obtain living specimens 

 of the other forms of these echinodermatous or radiated 

 creatures such as Spatangtis purpureus, Echinocyamus 

 pusillus, and Amphidotus cordatus, or the common Heart 

 Urchin, of which the dead and empty shells, with their spines 

 rubbed off, may frequently be noticed washed up and left 

 upon the sands. 



