52 EVENINGS AT THE MICROSCOPE. 



rovings, as well as to guard it from hostile assaults. The 

 animal is very sensitive, withdrawing its tentacles and 

 mantle, and bringing the valves of its shell together, on. 

 any shock being given to the vessel in which it resides. 

 It manifests, however, a wisely measured degree of 

 caution, for it does not actually close the valves, unless 

 it be repeatedly disturbed, or unless the shock be violent, 

 contenting itself with narrowing the opening to the 

 smallest space appreciable ; yet even then the two rows 

 of gem-like eyes are distinctly visible, peeping out from 

 the almost closed shell, the tw^o appearing like one 

 undulating row from the closeness of their proximity. 



If you are familiar with the pin-cushions which children 

 often make with a narrow ribbon round the edges of these 

 very Scallop-shells, you can scarcely fail to be struck 

 with the resemblance borne by the living animal to its 

 homely but useful substitute ; and the beautiful eyes 

 themselves might be readily mistaken for two rows of 

 diamond-headed pins, carefully and regularly stuck along 

 the two edges of the pin-cushion ribbon, — the ribbon itself 

 representing the satiny and painted mantle. A friend of 

 mine, to whom I was once showing this object compared 

 it, not inaptly, to a lady's ring set with diamonds. 



You will not fail to remark how the position of these 

 beauteous organs is suited for their most extensive useful- 

 ness consistent with their safety. In the ordinary condi 

 tion of the animal's expansion, and especially when it i& 

 about to make its sudden and vigorous leaps, the gem- 

 like points are so situated as just to project beyond the 

 margin of the shell. So that when we view the creature 

 perpendicularly as it lies, our eyes looking down on the- 

 convexity of the upper valve, the minute eyes are seen, all 

 round its circumference, just, and but just, peeping from 

 under its edge. It is clear that this arrangement secures 

 to them the widest range of vision with the least possible- 

 exposure. As Divine contrivance has been often most 



