MOLLUSC A. 



IS 



a magnifier these flutings can be seen to be covered by 

 a net-work of lines with partially transparent spots be- 

 tween them. 



Mix a Httle indigo with salt water, and pour a few 

 drops with a medicine dropper or glass tube on the 

 surface of the gills. If the oyster is living, the particles 

 will be seen to gather into threads, and pass down 

 the surface of the gill to the edge, and over this into a 

 channel along the outer edge (Figs. 7, 8). Here they 

 are joined to a larger thread of food which is moving 

 towards the four pointed flaps. Of course all the 

 minute plants and animals of every kind, of which 

 there are myriads floating in the water where oysters 

 are found, must be acted upon in the same way. They 

 are entrapped in the mucus, which is abundantly se- 

 creted by the surfaces of the gills, and moved forward 

 by the cilia or waving hairs which cover the surface 

 with a coat like the pile on velvet. These move so as 

 to force the combined mucus and particles to weave 

 themselves into threads, which are carried forward 

 until they come within the reach of the cilia coating 

 the canals that run along the edges of the gills. These 

 take them up, bind them together, and move the whole 

 forward as four larger threads which are finally received 

 between the two pairs of pointed flaps at the upper 

 end. Each pair of these embrace a pair of the gills 

 with their extremities, and receive the two large tlireads 

 of food which they have spun. 



These flaps may be seen by the naked eye to be 

 roughened by linear ridges on their inner surfaces, 

 which enable them to fit closely where in contact, and 

 also increases the area of surface for the development 



