THE MICROSCOPE. 119 



slowly about in the water, waving from side to side, as when first 

 noticed, spreading and closing its lip-extremity as if feeling for 

 something in the surrounding fluid. 



In farther examination of specimens I found that generally 

 the lip of the proboscis was clasped around the cephalic ends of 

 the gill-leaves, with the proboscis so bent as to look much like the 

 handle of a jug, and the slit of the lip turned toward the mouth 

 cavity. This is undoubtedly its normal position, and so placed for 

 the purpose of taking up such food as may be gathered by the gills 

 and passed along to the ends of their grooves, but there seems to be 

 no good reason for believing but what the lip can be unclasped at 

 will from the ends of the gills and the proboscis moved about freely 

 within the mouth cavity, as I found in several instances when the 

 shells had been removed. If then the young animal can in its 

 normal condition detach the lip from the ends of the gills and 

 thrust the proboscis about freely in the water within the mouth 

 cavity, it is undoubtedly for the purpose of gathering, which it 

 could do with ease, whatever food-particles it might encounter 

 floating about in the water, or in other words, to assist the 

 gills in gathering sufficient food for the growing body. It would 

 indeed seem necessary that some special modification of the body 

 should be required to aid in supplying food. In the free-swimming 

 state the active motion in the water brings about a quite rapid 

 change in the circulating medium and a corresponding large quan- 

 tity of food material is presented for the growth of the animal; in 

 the adult state the gills, with their numerous cilia in nearly constant 

 motion, are sufficient to supply all the food required, but during the 

 proboscis stage the animal has ceased its promiscuous wanderings, 

 becoming decidedly home-keeping and domestic in its economy, 

 hence to an important extent its food supply has been cut off, and 

 the gills are not yet in a sufficiently advanced condition to supply 

 this deficiency or to warrant their being relied upon alone as a 

 means of obtaining such supplies as are necessary. It may be con- 

 sidered thus as fairly certain that the proboscis is a modification of 

 the body, a contrivance designed to facilitate during the period of 

 incomplete gill action, the gathering of food-particles from the 

 water passing in and out of the mouth cavity. 



The young oyster would then have a double. chance of getting 

 ts food, or perhaps I ought to say the young oyster would thus be 



