HABITS OF ECHINI. 



Maxv of the Desinosticha, along coasts exposed to the action of the waves, 

 live- in cavities which they hollow out of the solid rock. This they do. not h\ 

 means of any solvent, but by mere mechanical action. They chisel ont with 

 their teeth the solid rock by incessant turning round and round, and keep 

 their cave, where they are frequently prisoners for the rest of their existence, 

 up to the size required by the growth of their test and spines by constant 

 gnawing. Along parts of the coast of France. Strongylocentrotus lividus 

 excavates in the solid granite. Caillaud has given an account of their 

 abodes. From the Azores the Museum possesses tin- same species, occurring 

 in cavities dug out of the solid rock. On the coast of California the common 

 Strongylocentrotus purpuratus occurs in the same way: we find long tracts 

 of the >hoiv. where this sea-urchin is common, completely honeycombed ami 

 pitted by cavities and depressions, in which they seek shelter against the 

 powerful surf continually beating against the rocks. The same species does 

 not excavate in sheltered places, where the sea-urchins can find protection 

 between the interstices of large fragments of rock, or Ledges more or less 

 sheltered from the more direct action of the open sea. Stimpson say- that 

 Coloboccntrotus is found at the Bonin Islands adhering, simply by their 

 suckers, to the perpendicular faces of rocks exposed to the full fury of a 

 Pacific Ocean swell. We must remember that the test of this genus forms 

 with its spines a Hat segment of a sphere, and that the close pavement of 

 polygonal spines presents but little surface to the action of the water. The 

 suckers of the actinal side are also very powerful and numerous. Some of the 

 species of Echinometra have the same habit of excavating a recess, in which 

 they grow. Echinometra Van Brimti is quite common at Panama in cavities 

 formed by the sea-urchin in the solid rock of the reef running out from the 

 town. Cidaris Thouarsii is also found in similar cavities in the same locality. 

 On the Florida reef, our common West India Cidaris has sometimes the same 

 habit of hollowing out a cave for protection, where greatly exposed, though 

 it is quite as frequently found free in the spaces between masses of rock. 



