Starfishes and Urchins. 63 



of the body itself, as is the carapace of a crab (Figs. 75 and 76). 

 This carapace, or test, to use a more correct term, is covered 

 with erectile spines. The urchins, like most starfishes, are five- 

 rajred, but the raj's are not free. Let us examine the large 

 Echinus escuhntus, a common urchin on our coasts. Its test 

 would be perfectly spherical but for a slight flattening of the 

 lower pole, in the middle of which the mouth is situated. It 

 is entirely covered with movable spines, attached by muscle 

 to knobs or tubercles, the larger spines, stout and pointed, 

 intermixed with others of more slender shape, each of the latter 

 ending in little pincers. These pincers, no doubt, serA'e to 

 capture small prey, but their mam function is to keep the surface 

 of the urchin clean, these creatures never becoming overgrown 

 with weeds or zoophytes, as is the case in so many sedentary 

 or slow-moving marine animals. As already mentioned, the 

 mouth is below. It is pro\aded with a complicated masti- 

 catory apparatus, bearing five strong teeth protruding through 

 the aperture. The vent is in the centre of the upper pole, 

 and close to it we find the perforated water-plate which we 

 have mentioned in the starfish. These apertures are best 

 seen on a specimen the spines of which have been removed, 

 or lost after death through decomposition of the soft tissues, 

 as on empty tests thrown up on the beach. We can then follow 

 the arrangement of the plates, in ten meridional zones, each 

 with two rows of plates, alternate zones consisting of plates 

 bearing small apertures, through which long tubular feet 

 protruded when the animal was alive, locomotion in the 

 urchins being effected in the same manner as in the starfishes. 

 The sexes are separate, and the roes of mature examples are 

 very large, affording an article of food in certain countries, 

 especially in Italy. Echinus cscidentns is of a brownish red, 

 sometimes inclining to violet, and grows to the size of a large 

 orange or grape-fruit. E. miliaris is a smaller species, with 

 a more flattened body about two inches in diameter. The 

 spines are relatively larger than in the edible species and of 

 an olive green with pinkish tips. Sirongylocentrotus lividiis, 

 often of a deep purple, occurs in great numbers in some 

 localities, in hollows made by them in limestone and other 

 rocks, often to a depth of ten inches. The excavations are 

 probably the result of mechanical action, and possibly due to 

 the constant movement of the spines, the ends of which may be 

 seen in many cases to be considerably worn. Our Sea-urchins, 

 of which there are a number of species besides those here 

 mentioned, are mostly inhabitants of deepish water near the 



