THE MICROSCOPE. 79 



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 in- 

 numerable myriads of little cilia, inconceivably small. To see them 

 well taxes the microscope. And how busy they are, as if each tube 

 might be a tiny trireme, manned through its whole length with the 

 little rowers, rowing, rowing, rowing. The function here is very 

 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 the mouth. Now, these branchiae, with cilia on their outer sur- 

 face, 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 filtered 

 water which has left the palpi, or lips, is now lashed by the cilia into 

 the holes of the tubules in the branchiae; 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 re- 

 vitalized blood is passed to its destination. 



4. Circulation. — 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 reverent spirit, put aside the veil and look in. Here 

 we see the little heart. On the right is its one auricle, receiving the 

 oxygenated blood from these ducts which connect with the gills; 

 and here is the ventricle into which the auricle discharges, and here 

 are two aortas by which the ventricle supplies the blood to be dis- 

 tributed through the one to the posterior parts, and through the 

 oilier to the anterior parts. It is a wonderful sight. In a freshly 

 opened oyster I have counted the pulsations at six in a min;ite. 

 Probably in a specimen just from the water it might be as high as 

 ten in a minute. Though I cannot do it now, it is not difficult 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 

 physiological systems are as well developed in an oyster as in a man. 

 But these systems now discussed have their analogical functions in 

 the life of the plant. Hence the three groups of organs, taken to- 

 gether, are often called by the physiologist the vegetal system. I 



