36 Lessons in Zoology. 



Lesson II. 



In the last leason ve have examined the spines, have foand the 

 month with its lantern, the tnbe-feet and the sieve, and have learned 

 how the tabe-feet can be extended beyond the spines. We begin 

 with a review of these points. 



The spines protect the searurchin against its enemies, 

 and are sometimes used in walking. If one is taken out 

 of the water and put on a table, it will try to walk on its 

 spines. 



Some species habitually nse the spines in this way. A pentago- 

 nal sea-nrohin that lives on coral reefs, covers itself with bits of 

 seaweed and pebbles, holding them on with its tnbe-feet, so that 

 bnt little of i'^s body is exposed, while walking on its spinos. Onr 

 common sea-nrchin often hides nnder a covering of sand and grave'. 



On alcoholic specimens, and on the under side of large, 

 well-preserved dried ones, children will see that the tube- 

 feet are arranged in five double rows, and later in the 

 lesson will connect this fact with the arrangement of the 

 plates of the shell. The forks can be best seen on the 

 disk of tough skin around the mouth, where they form a 

 circle. They are larger than those of the star-fish, three- 

 pronged, and mounted on handles (Fig. 4). They aie 



scattered everywhere among 

 the spines, but largest around 

 the mouth. It has been 

 found by experiment that 

 they will grasp a frond of 

 seaweed waving lightly over them in the water, and hold 

 it like so many tiny forceps till the suckers have had time 

 to fix themselves upon it. 



The remainder of this lesson is the most difficult part of the 

 work on the sea-nrohin, and should be oonduoted by the teacher 

 with the greatest patience and care. Though " Make baste slowly " 



Fie. 4 



