focus stands out in strong plastic relief; with the 

 monocular the image is flat. The general flexibility, 

 also, of the binocular now makes it the instrument 

 par excellence for the purpose at hand. So, setting 

 it before a three-gallon glass tank filled with salt- 

 water and the usual seaweeds, and containing no 

 creatures more imposing to the casual glance than 

 a couple of common green-crabs, I bring it to bear 

 upon an empty oyster-shell half-imbedded in the 

 gravel on the bottom. The powerful beam of my 

 laboratory lamp is so fixed that its sharp circle of 

 light — less than four inches in diameter — floods 

 the shell with dazzling brightness. All other lights 

 in the room are switched off; I settle into a chair 

 before the illuminous shell, and in the outer dark- 

 ness prepare for a cinema all my own. 



I have not selected this shell without considera- 

 tion. It is old and rotten. Its surface, once pitted 

 over the greater part by the perforating solvent of 

 a boring sponge, is now encrusted with the scurf of 

 dead worm tubes and empty barnacle shells. The 

 only visible signs which it betrays of inhabiting 

 life are the inconspicuous, lace-like patch of cal- 

 careous film, covering the space of about a nail's- 

 breadth near the rim of the shell and indicating 



[131] 



