52 mTRODUcnox to zoology. 



in the deep." And this feeling increases with the increased 

 minuteness of our examination. " In a moderate-sized Urcliin 

 I reckoned," says Mr. Forbes, " sixtv-two rows of pores in 

 each of the ten avennes. Now, as there are three pairs of 

 pores in each row, their number multiplied by six, and again 

 by ten, would give the great number of 3,720 pores; but, as 

 each sucker occupies a pair of pores, the number of suckers 

 would be half that amount, or 1,860. The structure in the 

 E.:;g-urchiu is not less complicated in other parts. There are 

 above 300 plates of one kind,, and nearly as many of another, 

 all dovetailing together with the greatest nicety and regularity, 

 bearing on their surfaces above 4,000 spines, each spine perfect 

 in itself, and of a complicated structure, and having a free 

 movement on its socket. Truly the skill of the Great Archi- 

 tect of Nature is not less displayed in the construction of a 

 Sea-urchin than in the building up of a world!" 



Respiration is secured in these animals by the free admis- 

 sion of sea-water through tiie pores in the external coA'ering, 

 aad by its propulsion, by means of cilia, over every portion 

 of the body. A large portion of the interior of the shell is, 

 at certain times, occupied by vessels filled with the ova, which, 

 in the Mediterranean and elsewhere, are much prized as an 

 article of food ; but, at other times, the ordinary observer finds 

 in the interior only a tube wound twice round the circum- 

 ference, and containing the stomach and intestine {Fig. 34). 

 In every step we make towards a knowledge of the structure 

 and liabits of these animals, we experience a feeling of surprise 

 and pleasure at the peculiarities they exhibit. Thus, on one 

 occasion, we had cut horizontally into two nearly equal paits 

 a large Sea-urchin, for the purpose of examining the intestines 

 and ovaries. These being removed, the shell was thro«-n ou 

 the deck of our little vessel, as being no longer of any service. 

 It chanced, however, that we afterwards picked up tlie parts 

 and placed them in a shallov/ vessel of sea-water. To our 

 ■surprise, the suckers were soon extended, and the animal 

 walked about, apparently as unconcerned as if the loss of 

 intestine and ovaries had been an every-day occurrence. 



At one extremity of the alimentary canal is a singular 

 apparatus, which performs the functions of teeth and jaws, 

 and which, in its detached state, is known as " the lanthorn 

 of Aristotle." Any teeth, fixed in sockets as ours ai'e, would 

 speedily be worn away by their action on the shell-fish, &c. ; 



