SEA-URCHINS. 185 



CHAPTEE XVIII. 



SEA-URCHINS. 



PROBABLY most visitors to the seaside are more or less 

 familiar with the shells of those marine creatures commonly 

 known as sea-urchins, or sea-eggs, this acquaintance being 

 usually due either to finding them cast up on sandy 

 beaches, or to seeing them offered for sale by the vendors 

 of curiosities and natural history objects. In many 

 instances it is probable that the acquaintance ends here, 

 although in others these objects may have been submitted 

 to a fuller examination ; but, in any case, we venture to 

 say it is comparatively few who have studied them with 

 the care and attention that their beauty of form and pecu- 

 liar structure demands, and still fewer who know anything 

 about their history in past times. Those, however, who 

 care to take up the subject will find it one of more than 

 usual interest, and we accordingly propose in this chapter 

 to place before the reader some of the leading features 

 and peculiarities of these creatures, which will form 

 stepping-stones for those inclined to proceed further with 

 their study. 



To begin with, sea-urchins take their name from the 

 array of movable spines with which the shell is covered 

 during life, and which suggest comparison with those of 

 the true urchin, or hedgehog. The shell, as it is commonly 

 called, will, indeed, be the portion of the animal to which 

 alone our attention will be directed, since it is only this 

 part that is capable of preservation in a fossil state. We 

 must, however, state at the outset that, as this so-called 

 shell does not by any means correspond in structure with 

 the shell of a mollusc, it is found more convenient to give 

 it a different name, and the term test has accordingly 

 been selected. Moreover, since the name sea-urchin is a 

 somewhat long one, we may conveniently abbreviate it to 

 urchin, unless we prefer to use the more technical term 

 Echinoid. 



There is great variety in the form of the hard calcareous 



