156 Secrets of the Ocean [FOURTH WEEK 



truding their whole stomach and thus engulfing their 

 victim. The urchins strain and stretch with their innum- 

 erable sucker-feet, feeling for something to grasp, and in 

 this laborious way pull themselves along. The mouth, 

 with the five so-called teeth, is a conspicuous feature, 

 visible at the centre of the urchin and surrounded by the 

 greenish spines. Some of the starfish are covered with 

 long spines, others are nearly smooth. The colours are 

 wonderfully varied, red, purple, orange, yellow, etc. 



The stages through which these prickly skinned animals 

 pass, before they reach the adult state, are wonderfully 

 curious, and only when they are seen under the microscope 

 can they be fully appreciated. A bolting-cloth net drawn 

 through some of the pools will yield thousands in many 

 stages, and we can take eggs of the common starfish 

 and watch their growth in tumblers of water. At 

 first the egg seems nothing but a tiny round globule of 

 jelly, but soon a dent or depression appears on one side, 

 which becomes deeper and deeper until it extends to the 

 centre of the egg-mass. It is as if we should take a round 

 ball of putty and gradually press our finger into it. This 

 pressed-in sac is a kind of primitive stomach and the en- 

 trance is used as a mouth. After this follows a marvellous 

 succession of changes, form giving place to form, differing 

 more in appearance and structure from the five-armed 

 starfish than a caterpillar differs from a butterfly. 



For example, when about eight days old, another 

 mouth has formed and two series of delicate cilia or swim- 

 ming hairs wind around the creature, by means of which 

 it glides slowly through the water. The photographs of 



