ECHINODERMATA. 
291 
k>ut the creature always directed its spines in the direction of the 
°hject which threatened it, whether it was in the water or out ot it.” 
®- e satisfied himself that these animals certainly could see, and that 
ttieir 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 pro- 
dded the Echinidas, appear to have been insufficient, inasmuch as these 
v ®i - y spines, in order to secure the safety of the animal, are gifted with 
*ke power of hollowing a dwelling for themselves out of solid rocks of 
Pke hardest material, such as granite and sandstone. They fix themselves 
k* 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 
mdi'eiieh themselves in it, with their spines and their threatening 
pikes levelled to protect them from all external assaults. To M. 
^ a ilaud, the conservator of the museum of Nantes, we are indebted 
,rj r an excellent account of the manner in which this buccal appa- 
mtus is made to operate. “ The Lantern of Aristotle, says this 
H uthor, “ forms the mandibnllary apparatus ; the teeth are five in 
mitnber, and they may as well receive the denomination of a series of 
S ' dv >’s and picks as of teeth, for they are surprisingly adapted to the 
® x cavation of holes in the hardest rock. These five picks are about 
l ke eighth of an inch long, and they serve the sea-urchin at once as 
^sticators and excavating implements. In opening the jaws, these 
teeth strike the stone forcibly rather than scrape it.” This 
Pfoperty of hollowing their dwelling out of the solid rock appears, 
°Wever, to belong to only a small number of the Ecliinidm ; most of 
kem are content to hide themselves under the stones, while the 
s P e cies having the spines slender and the shell very thin bury them- 
8e * v es in the sand, with which they cover themselves entirely, leaving 
a small hole to breathe through. The Spatangus, which is 
m'tiislied with short thick spines on the under part ol its body, 
^kich spread out at the extremity like the channel ot a spoon, 
Proceeds with its mining operations as follows : — According to Mr. 
' Nathan Franklin, “ Figure to yourselves, reader, the animal on the 
S6a '®hore. He commences his operations by turning the lower spines 
11 s,,e h a manner as to form a hollow on the sand bank, m which he 
Bln ks by his own weight, but as he sinks, a great number of the 
u 2 
