68 



THE AMERICAN MONTHLY 



[April, 



look at this large diagram. I have 

 torn ofif the right side of the cloak, 

 thus exposing the animal, which, with 

 the flat shell removed, is represented 

 as lying in the round or dished shell. 

 This leaves the prominent organs ex- 

 posed. The edge of the pallium is 

 beset with rather coarse, fleshy hairs, 

 which are cilia. As there are two 

 edges, they make a double fringe. 

 When the shell is a little bit open 

 this ciliated fringe is slightly pro- 

 jected, and is called the beard. The 

 two fringes keep up an incessant vi- 

 brating action which sets the water 

 flowing in between them ; and another 

 contrivance, soon to be described, car- 

 ries the food-laden water forward over 

 the body, or ventral side of the ani- 

 mal, up to this spot near the hinge, 

 where it is received on the edges of 

 four flattish lips, the mouth being be- 

 tween the two pairs. We may call 

 these organs palpi, or labial fingers ; 

 for they assort this food from the water, 

 which done, the water thus filtered is 

 passed backward on the dorsal side, 

 by innumerable and invisible lashes. 

 I said invisible, for it requires a high 

 power of the microscope to detect 

 this mystic mechanism. Analogy 

 compels us to believe that it is a simi- 

 lar ciliated movement which carries 

 the food down the alimentary canal. 



" Perhaps even more beautiful is 

 the respiratory system. Here, in the 

 posterior part of the animal, so as to 

 be near the water, are the branchial 

 plates, or gills. Like the palpi, they 

 are in two pairs, one pair for the left 

 side and one for the right. They 

 comprise an infinity of little tubes, 

 so small that the unaided eye cannot 

 distinguish them. Each tubule has 

 on one side a row of holes, as if 

 it might be a tiny flute. On these 

 little tubes are innumerable myriads 

 of little cilia, inconceivably small. 

 To see them well taxes the micro- 

 scope. And how busy they are, as 

 if each tube might be a tiny tri- 

 reme, manned through its whole 



length with the little rowers, rowing, 

 rowing, rowing. The function here 

 is vc-y strange, because it seems two- 

 fold. All over the animal are these 

 cilia, and all are lashing the food- 

 laden water to the anterior, where is 

 ihe mouth. Now, these branchiae, 

 with cilia on their outer surface, lend 

 their aid to produce this general 

 movement of the water ; but to the 

 branchiae this is only a secondary 

 function. There are millions of these 

 tiny cilia between these gill-flaps, and 

 their primary function is the aeration 

 of the blood. To effect this the fil- 

 tered water which has left the palpi, 

 or lips, is now lashed by the cilia into 

 the holes of the tubules in the 

 branchi^ ; here the air is taken out, 

 and the oxygen eliminated, and the 

 now carbonated water is passed on to 

 the cloacal region, while the opal-hued 

 and oxygenated or revitalized blood is 

 passed to its destination. 



"This brings us to the circulatory 

 system. Looking at our diagram we 

 see here a dark crypt, a little mystic 

 chamber. It is the pericardium, or 

 receptacle of the heart. This vital 

 crypt is covered with a thin membrane 

 or translucent caul. Let us in a rev- 

 erent spirit, put aside the veil, and 

 look in. Here we see the little heart. 

 On the right is its one auricle, receiv- 

 ing the oxygenated blood from these 

 ducts which connect with the gills; and 

 here is the ventricle into which the 

 auricle discha^es, and here are two 

 aortas by which the ventricle supplies 

 the blood to be distributed through 

 the one to the posterior parts, and 

 through the other to the anterior parts. 

 It is a wonderful sight. In a freshly 

 opened ovster I have counted the pul- 

 sations at six in a minute. Probably 

 in a specimen just from the water it 

 might be as high as ten in a minute. 

 It is not diflicult to demonstrate that 

 the oyster has a complete apparatus of 

 arteries and veins. 



"Thus it seems that so far as its 

 necessities reach, the three physiolog- 



