ECHINODERMATA. 289 



But the creature always directed its spines in the direction' of the 

 object which threatened it, whether it was in the water or out of it." 

 He satisfied himself that these animals certainly could see, and that 

 their spines served them as a means of defence. 



These wonderful spines, this calcareous envelope, this armour so 

 marvellously studded, with which nature has so bountifully provided 

 the Echinidae, appear to have been insufficient, inasmuch as these 

 very spines, in order to secure the safety of the animal, are gifted with 

 the power of hollowing a dwelling for themselves out of solid rocks of 

 the hardest material, such as granite and sandstone. They fix themselves 

 to its surface by means of their tentacles ; they make an incision by 

 means of their strong teeth, removing the debris with their spines 

 as fast as it is produced. When the hole is large enough, they 

 entrench themselves in it, with their spines and their threatening 

 pikes levelled to protect them from all external assaults. To 

 M. Caillaud, the conservator of the museum of Nantes, we are indebted 

 for an excellent account of the manner in which this buccal appa- 

 ratus is made to operate. " The Lantern of Aristotle," says this 

 author, " forms the mandibullary apparatus ; the teeth are five in 

 number, and they may as well receive the denomination of a series of 

 saws and picks as of teeth, for they are surprisingly adapted to the 

 excavation of holes in the hardest rock. These five picks are about 

 the eighth of an inch long, and they serve the sea-urchin at once as 

 masticators and excavating implements. In opening the jaws, these 

 five teeth strike the stone forcibly rather than scrape it." This 

 property of hollowing their dwelling out of the solid rock appears, 

 however, to belong to only a small number of the Echinidae ; most of 

 them are content to hide themselves under the stones, while the 

 species having the spines slender and the shell very thin bury them- 

 selves in the sand, with which they cover themselves entirely, leaving 

 only a small hole to breathe through. The Spatangus, which is 

 furnished with short thick spines on the under part of its body, 

 which spread out at the extremity like the channel of a spoon, 

 proceeds with its mining operations as follows, according to Mr. 

 Jonathan Franklin. " Figure to yourself, reader, the animal on the 

 sea-shore. He commences his operations by turning the lower spines 

 in such a manner as to form a hollow on the sand bank, in which he 

 sinks by his own weight ; but as he sinks, a great number of the 



