222 THE ANIMAL KINGDOM. 



these fine plates are called ambulacral plates, and are not in 

 one piece ; closely examined each plate consists of many 

 smaller ones, no less than 300 of them in those five divi- 

 sions, and again in the avenues between the pores there are 

 300 more. 600 plates, besides the 4000 spines and count- 

 less pedecilarise in the outward form of the common Sea- 

 urchin ! 



The structure of the mouth is one which has long been 

 the wonder and admiration of naturalists, and was com- 

 pared by Aristotle to a lantern without a skin, from whence 

 it has derived the name of Aristotle's Lantern. Again we 

 see the number five, in five jaws, each with a long sharp 

 tooth converging in the centre, close to the mouth, and the 

 framework of these jaws consists five times jive pieces, 

 moved by six times five muscles, working with great power 

 the jaws of this little animal, who feeds on any dead fish 

 or flesh it can attain, eating also young crabs with great 

 greediness, and catching them with the suckers which 

 surround the mouth. The opposite end of the shell is 

 occupied by five ovarian plates, in each of which there is 

 an aperture by which the eggs are excluded; they are 

 strengthened by transverse bands inside, and again sepa- 

 rated bjfive smaller plates which bear each a little red eye. 

 The internal anatomy I shall not enter upon ; enough is 

 written here to give much interest to the various sections 

 of Echinus spines which we purchase as microscopic objects, 

 and which are sometimes glanced at as very pretty crochet 

 patterns. 



OBJECTS FOR THE POLARISCOPE. 

 POLARIZED LIGHT. 



The possession of a polarizing apparatus with a good 

 microscope is a source of much gratification even to the 

 unscientific, inasmuch as common substances are glorified 

 thereby in a marvellous way. My parish boys declared 

 they had no notion their cows' horn was so beautiful, and 

 some of them wished audibly for a waistcoat like the elytra 



