58 STAR-FISHES AND SEA-URCHINS. 



ancient Star- Fishes on stems ; but, as they are rare and 

 are not found in our waters, I will not attempt to de- 

 scribe them to you. 



Let us look now at the Sea-Urchin, or Sea- Egg 

 (No. 43.) Though very different in appearance from 

 a Star- Fish, it is almost exactly like it in the number and 

 arrangement of its parts. The arms which are stretched 

 out in a five-rayed Star- Fish; if drawn together and joined 

 at the points, would make a Sea-Urchin ; the rows of 

 suckers and spines, arranged along the five rays in the 

 Star- Fish, are arranged in alternate rows up and down 

 the surface of the Sea- Urchin ; the five eye-specks at 

 the extremity of the rays in the Star-Fish are drawn 

 close together on the summit of the Sea-Urchin, and 

 the mouth is placed at the centre of the lower side in 

 the Sea- Urchin, as in the Star- Fish ; but it has five little 

 teeth not to be found in the Star- Fish. The tubes car 

 ried along the arms of the Star-Fish follow the line of 

 the rays in the Sea-Urchin, and the little sieve through 

 which the water enters them is on the upper side of 

 the body, between two of the rays. The little forks, 

 which have three prongs, instead of two as in the Star- 

 Fish, are scattered over the surface between the spines. 

 In the Sea- Urchin, they are often used to cleanse the 

 surface of the body, and you may see the rejected bits 

 of food, for instance, caught in these little forks, and 

 passed along from one to the other down the sides of 

 the body, till they are dropped off into the water.* 



You may form some idea of the way in which the 

 difference in the outline of a Star- Fish and a Sea-Urchin 

 is produced, by making five equal divisions on the 



For further details, see "Sea-Side Studies" (A. Agassiz). 



