724 THE PIPER-URCHIN. 



pebbles, that it is almost entirely hidden under the superincumbent mass. A specimen 

 thus enveloped is seen at the lower part of the illustration. 



Immediately under the first-mentioned specimen is a curious figure which demands 

 some explanation. This is the internal skeleton of the sea-urchin removed from the 

 body, and comprises the complicated and beautiful machinery by which the Echinus 

 is enabled to cut to pieces the hard substances on which it feeds. It will be seen, by 

 reference to the illustration, that there are five long stripes of bony substance, which, 

 on examination, are found to bear a wonderful resemblance to the incisor teeth of the 

 rodent animals, being of enamel-like hardness at their points, and soft and pulpy at their 

 bases. Like the rodent teeth, moreover, they are continually worn away at their points, 

 and as continually pushed forward by fresh growth from behind. 



Indeed, a very good idea of the structure of these jaws may be obtained by taking five 

 incisor teeth of the rabbit, and arranging them so that their points touch each other and 

 their bases diverge. Let these be bound together by the muscles necessary for their 

 peculiar movement, and they then will form a figure almost identical with the jaws of the 

 Echinus. This curious apparatus was likened by Aristotle to a lantern, and has thence 

 derived the popular name of Aristotle's lantern. 



It will be seen that a sort of five-sides pyramid is formed by the entire apparatus, and 

 that at its base are a number of stout levers which assist in the movements. This 

 remarkable object ought to be examined while quite fresh, as the muscular bands are 

 easily affected by drought, shrivel into thin thread-like bands, and quite fail to convey a 

 correct idea of their real shape and duty. 



Below the jaws is seen a magnified view of one of the large movable spines, showing 

 the projecting ball on the surface of the shell and the socket in the base of the spine. 

 The two curious objects on the rock, at the right hand of the illustration, represent the 

 strange appendages to the shell, which are termed Pedicillariae, and are given in a 

 magnified form in order to show their structure. The Pedicillariae are found scattered 

 among the spines, and placed upon the shell, and are of very minute dimensions. They 

 are of calcareous substance, and are furnished at their tips with a three-bladed head, the 

 valves of which are continually opening and closing, and presenting the appearance 

 which is exhibited in the illustration. 



Pedicillariae are found upon many other Echinodermata, and their object is very 

 doubtful. The most rational theory seems to be that they are placed there in order, by 

 their perpetual movements, to keep the shell clear from the various algas that are sure to 

 grow upon any marine substance that is not protected from their approaches, as also to 

 perform the same office towards the young serpulae, molluscoids, and zoophytes which fill 

 the ocean with their multitudinous hosts, and settle upon every object that affords even a 

 short period of quiet. 



ON the next illustration are seen two views of the same object, in order to show the 

 great size to which the spines attain in some species. 



The genus to which the PIPER-URCHIN belongs can always be recognized by the 

 enormous comparative size of the tubercles sustaining the spines and the parallel rows of 

 ambulacra. The tubercles are not perforated. In the illustration, one figure shows the 

 Piper-urchin as it appears when entire, and the other exhibits its aspect when the spines 

 are removed, so as to show the large size and bold protuberance of the spine-bearing 

 tubercles. 



The members of the genus Cidaris are mostly found in the hotter parts of the world, 

 and are plentiful in the Indian Seas. The spines of several of the species have been 

 made serviceable in the cause of education, being found to make excellent slate-pencils 

 after being calcined. The missionaries have the credit of making this useful dis- 

 covery. 



The food of the Echini in general seems to consist of various substances, both of an 

 animal and vegetable nature. Fragments of different sea-weeds have been found in the 

 digestive cavity, as also certain portions of shells, which seem to prove that the Echinus 

 had fed upon the molluscs, and broken their shells in pieces with its powerful jaws. 

 The precise mode of feeding is not exactly ascertained ; but it seems likely that the 



