ANIMAL GLOBES 183 



by transverse joints into a great number of plates, arranged 

 with geometric regularity. The mouth of the Echinus is 

 beneath, at the meeting-place of all the bands. The shell 

 grows by the continual addition of fresh material to all 

 the edges of all the plates, and it is singular that the 

 resulting figure should be one of such perfect symmetry. 



What are urchins, and are there any urchins besides 

 sea-urchins ? Urchin originally meant a hedgehog, then 

 it came to signify a bogey, and lastly a child. The word 

 is got, through the French herisson, from the Latin ericius, 

 and may be translated bristly. Oursin, the French name 

 for the sea-urchin, notwithstanding the similarity of the 

 sound, has nothing to do with herisson, but means little 

 bear (ours). 



The hard and jointed shells of crustaceans and insects 

 lend themselves easily to this mode of defence. Woodlice, 

 which are terrestrial crustaceans, roll themselves up when 

 alarmed, and one kind has even been named Armadillo 

 (to the confusion of zoological speech). Hairy caterpillars 

 often roll themselves up for defence, or to break the shock 

 when they find themselves falling to the ground. The 

 ruby- wasps (Chrysididge), which live at the expense of 

 stinging Hymenoptera, can roll themselves up into im- 

 penetrable balls. 



Most snails are protected by spiral shells, but in the 

 Chitons the shell is neither spiral nor in one piece ; it 

 consists of eight valves, one behind another. The valves 

 are flexibly connected, and can be rolled up. The segmented 

 shell also enables the animal to accommodate itself to 

 the inequalities of the rocks to which it clings. 



The winter-eggs of a freshwater sponge and the micro- 

 scopic bodies of many Foraminifera and Polycystina are 

 defended by radiating spines ; sometimes these spines 

 seem to have other uses than defence. 



We have in this country three common Insectivores, 

 the hedgehog, the shrew and the mole. Though closely 

 related, they are very unlike in mode of life, and seem 



