SEA-URCHINS, STARFISH, AND BRITTLE-STARS 127 



only in the great depths, and the sea-cucumbers are rare 

 between tide-marks, at least on the East Coast; so that 

 practically our studies of the group must be confined to the 

 starfishes, brittle-stars, and sea-urchins. Even of these we 

 have very few littoral species, so there should be no diffi- 

 culty in learning to recognise all the common forms. We 

 may conveniently begin with the starfishes, in which the 

 body is distinctly star-shaped, but has often more than five 

 arms, has an open ambulacral groove (or groove containing 

 the tube-feet) on the ventral surface of each arm, or ray, 

 and has both the digestive and the reproductive organs pro- 

 longed into the stout arms. 



The common starfish, Asterias rubens, is perhaps the most 

 abundant form, and we may describe its peculiarities first. 

 As in most shore Echinoderms the colour is very variable 

 red, orange, purple being the commonest tints. The limy 

 plates in the skin are netted, or reticulate, and bear numerous 

 small spines. A row of these spines runs down the middle 

 of each arm, but in very large specimens this regularity of 

 arrangement is not obvious near the ends of the rays. 

 Scattered among the spines are pedicellarice, or little stalked 

 forceps. The tube-feet are arranged in four rows, and the 

 sides of the ambulacral groove are furnished with two rows 

 of spines. To the outer sides of these spines there are 

 three rows of closely crowded spines. We have already 

 noticed the frequent occurrence of specimens showing re- 

 generation of lost or injured parts. In some places this 

 starfish is extraordinarily common, and occurs in numbers 

 in every rocky crevice. St. Andrews and Joppa may be 

 specially mentioned as spots where I have found it very 

 abundant. On the West Coast there occurs, in addition, 

 the larger and handsomer Asterias gladalis, which has 

 larger and more numerous spines, arranged in several regular 

 rows down the arms ; but this does not occur on the East. 



Almost equally common with Asterias rubens is another 

 smaller five-rayed starfish which occurs in many colour 

 varieties purple, purplish red, pure red, orange, all being 

 common. It is more compact in shape than the common 

 starfish, and contains so much lime that it is exceedingly stiff 

 and does not droop flaccidly when lifted up as that animal 

 does. This is Henricia sanguinolenta, and it has also a 



