i 4 THE POPULAR SCIENCE MONTHLY. 



The heart, constricted at the middle like the former silk purses of 

 the ladies, is shown in place. The constriction separates the auricle 

 and the ventricle. And so even an oyster has three sets of circulating 

 organs, the heart with its double set of functions, and the arteries and 

 veins. And this little organ beats with regular pulsations. That lit- 

 tle auricle receives the blood from the gills, and that tiny ventricle is 

 the vital force-pump that propels it into the arteries. " From the cap- 

 illary extremities of the arteries it collects again into the veins, cir- 

 culates a second time through the respiratory organ, and returns to 

 the heart as arterial blood." The color of the oyster's blood is a pale 

 bluish white in fact it may be called opaline. Our oyster, then, is 

 not a heartless thing. If you open it with care and skill, as would 

 the naturalist, you may see and count the throbbings of its tiny heart. 



In its proper place is seen the liver, which is always a large organ 

 in the mollusca, or so-called shell-fish. It is true that this organ in the 

 oyster secretes bile, and doubtless in large quantities. It is not prob- 

 able, however, that this organ, though large, ever performs a meta- 

 phorical function, for it is very doubtful whether the oyster ever gets 

 up the amount of emotion necessary " to "stir one's bile." To the fast 

 liver this oyster-liver is every thing. The secret is just here : this 

 secretion of the liver is the real appetizer of the feast. This oyster- 

 bile is both gustatory and digestive. It excites the glands of the 

 palate and the secretions of the stomach. 



The part indicated by the word muscle is the portion through 

 which the knife, is passed when opening an oyster. In popular par- 

 lance it is sometimes called the " eye," and by some the " heart ; " 

 terms which, thus applied, are without meaning. It is the adductor 

 muscle, and is the organ with which the oyster pulls-to its doors. 



To sum up these considerations of the oyster's physiology, we see 

 that, to the full extent of its necessities, it has distinctive sets of or- 

 gans for the performance of the three classes of functions carried on in 

 our own organization, namely, ingestion, respiration, and circulation. 



The Oyster's Shell. The toughest part of the oyster is the 

 adductor muscle (Fig. 7). The office of this large, strong muscle is to 

 pull-to and keep shut the great doors of the house. And a very cu- 

 rious bit of mechanism is subsidiary to this action. At the upper part 

 of the cut is seen the hinge, a white spot with a dark curve below it. 

 This dark curve is the hinge-ligament. It is a dark substance which 

 fills up the pit or depression near the hinge. In the living animal it 

 is wonderfully like gutta-percha black, tough, and elastic. Let us 

 attempt to explain its use to the oyster. Although this mollusk has a 

 strong muscle with which to close its valves, it has not any with which 

 to open them. Now, supposing we should take a lady's writing-desk, 

 and, between the hinges at the back of the lids, should insert a piece of 

 India-rubber, then should press down the lid, and turn the key ; it is 

 plain that the bolt of the lock now keeps the lid down, which could 



