180 RAMBLES OP A NATURALIST. 



the sides of its head, are protruded and act like 

 the two paddle-wheels of a steam-boat. 



With the view of directing its course, the Poly- 

 ophthalmian is provided on its head with three eyes, 

 each of which is furnished with two or three volu- 

 minous crystalline lenses, very easy of recognition. 

 Besides this, on each side of the rings of its body 

 there appears on either side a red point, very similar 

 to those of certain of the Amphicorae. On dissection, 

 we find that each of these points receives a large 

 nerve issuing from the ganglion or ventral nervous 

 centre corresponding to it. By the help of the 

 microscope, we can see that this nerve penetrates 

 into a mass of pigment, which encloses a spherical 

 crystalline lens, and we now see that the textures 

 lying before it have undergone a modification by 

 which they are rendered more completely and equa- 

 bly transparent. In a word, we can no longer 

 doubt that these red points, which are placed on the 

 sides and along the whole length of the body, are 

 true eyes, receiving their optic nerves from the 

 abdominal nervous centres, and having no direct 

 connection with the brain. 



This result, however strange it may appear, is not 

 the only one of the kind by which modern science has 

 been enriched. The Mollusca furnish us with several 

 facts of the same nature. Most of our readers are 

 no doubt acquainted with the Pecten, which is com- 

 monly known as St. James's or the pilgrim's shell. 

 The animal which inhabits this shell somewhat re- 

 sembles the oyster, and possesses like the latter a 

 mantle or thin covering of living tissue, which lines 



