164 THE HALL OP SHELLS. 



upon which the eyes are located can be drawn 

 down through the tubes, as the finger of a 

 glove is drawn in. The tubes are so trans- 

 parent one is able to see the black eye as it 

 descends through the shortening tube to the 

 little case under the skin of the head where it 

 is safe. 



" These little tentacles or eye stalks are so 

 sensitive of danger that the least impression is 

 telegraphed through the nervous organism of 

 the animal, and in an instant the eyes are out 

 of sight, and if danger still seems imminent, the 

 cautious little creature glides quickly into his 

 fortress. 



" As proof of the clear vision of snails it is 

 affirmed that they will go around obstacles in 

 their path, and they appear to be attracted by 

 bright colours. 



" Among bivalves tiny specks have been 

 detected near the borders of the mantle, some 

 shining like jewels, others too small to be per- 

 ceived except by a most careful scrutiny with 

 a strong lens. These are supposed with good 

 reason to be eyes. It has been observed that 

 a sea urchin will sometimes turn its spines as 

 if for self-defense in the direction in which a 

 hand approaches to capture it. 



" The razor fish, even when buried in the 



