THE STRUCTURE OF THE OYSTER. 73 



The lower folds of the mantle then become united on the 

 right side, nearly opposite to the muscular ligament, and 

 they form an entrance to the interior of the branchiae, or 

 breathing organs, which has been termed the branchial 

 porch. The mantle is free throughout its circumference, 

 except a part of its margin on the straight, side, where it 

 forms a kind of a hood. 



The oyster has a mouth, placed at the narrowest part 

 of the body a simple orifice with no kind of teeth, but 

 bordered by four thin lips, ranged on the two sides of the 

 aperture, and is represented covered by a part of the 

 mantle. The tube called oesophagus, from two Greek 

 words meaning " I eat," and "to carry," and more com- 

 monly the gullet, is extremely short, so that in such 

 creatures the mouth appears to open into the stomach. 



The stomach is a kind of bag, placed immediately 

 behind the opening of the mouth ; and when, in any 

 instance, the stomach is cut open, it will show the apertures 

 of several large vessels, by which the bile is conveyed from 

 the liver an organ which entirely surrounds the stomach. 



The liver is very large, of a greenish and sometimes a 

 dark chocolate colour. Externally it exhibits a regular 

 series of equal-sized granules, which may be shown by 

 boilinsr the oyster, and then tearing off its loosened 



O J 



external covering. Internally it presents arborescent 

 vessels, which converge into excretory ducts, as they 

 approach the stomach. The minute vessels of the liver 

 assume a grape-like figure, common to all the higher order 

 of animals. 



The intestine is comparatively short, bending on 

 itself, winding round the liver, and terminating at the part 

 opposite the mouth. 



