62 



COLOUR, FORM, AND MOVEMENT. 



The Case of the Starfish. 



The starfish deserves further notice. An example of the 

 common variety has five similar rays regularly arranged. 

 There are five cuts which seem to give an equal division, 

 and all the pairs appear the same. But on close examina- 

 tion we find that on the central disc there is a definite 

 rounded plate opposite the angle between two rays. It is 

 rather small, but it is certainly not trivial ; it is a definite 



Fig. 7. Starfish. The larger figure shows the under, the smaller the upper side. 

 M, the madrepore, the spot referred to in the text which gives the line of 

 bilateral symmetry. Other references are m, mouth ; ./., feet ; a.g., the ambu- 

 lacra! groove on underside of the ray. 



organ leading into the water system of vessels, and it 

 destroys after all the radial symmetry. A line through 

 this plate and through the odd ray opposite gives the true 

 dividing line of bilateral symmetry. But while emphasis- 

 ing a point like this, we need not minimise the undoubted 



