HEDGEHOGS. 41 



common hedgehog the " British porcupine " ; but, on the 

 other hand, it* we allow similarities in external appearance 

 to be our guide in nomenclature, there are just as good 

 grounds for applying the latter title to the hedgehog as 

 there are for giving the names of golden or Cape mole, 

 sand- mole, mole-vole, and marsupial mole to four of the 

 creatures noticed in the last chapter. Our ancestors, to 

 whom the hedgehog was commonly known as the " urchin," 

 went, however, a step further than this, and, from the 

 resemblance of its spine to those of the mammal, gave 

 the name of sea-urchin to the Kchinus, a title which has 

 stuck to it ever since. Systematic zoologists need not 

 then wax so wroth as we have known them do when the 

 name of " British porcupine " is applied to the urchin, 

 seeing that the analogies of nomenclature are sufficient 

 to justify its use. As the sea-urchins come most dis- 

 tinctly under the title of spiny animals, it may be 

 mentioned here tha.t, although the spines of the common 

 British species are not unlike those of the hedgehog, yet 

 their structure is totally different. Thus, whereas the 

 spines of the mammal are of a horny nature, those of 

 the invertebrate owe their solidity to the presence of 

 carbonate of lime, and always break with the characteristic 

 oblique fracture of the mineral calcite. Moreover, 

 whereas the spines of the hedgehog are implanted in its 

 skin, those of the sea-urchin are entirely external, being 

 movably attached by their hollow bases to knobs on the 

 surface of the shell or " test." Whether our worthy 

 ancestors believed that the land and sea-urchins were 

 connected by ties similar to those which in their estimation 

 affiliated barnacle-geese to barnacles, or how the name 

 ''urchin" came also to indicate a child, we are quite 

 unaware. 



In place of terminating in sharp points, by which they 

 are but loosely attached to the skin, like those of the por- 

 cupine, the spines of the hedgehog terminate interiorly in 

 small knobs, which are placed beneath the skin, and may 

 thus be compared to pins stuck through a piece of soft 

 leather. Beneath the skin lies a layer of muscle known 

 as the panniculus carnosus ; and it is by the action of this 



