156 OYSTERS, AND ALL ABOUT THEM. 



sidered to be in full flavour until September. The period 

 of its longevity is not known. It is said to be in prime 

 condition from the fourth to the seventh year, and rarely 

 to live beyond its fifteenth year. If the numerous laminae 

 or plates of which the shell is composed denote the marks 

 of annual growth, some individuals must attain a very 

 venerable age ; but these are formed inwardly, instead of 

 outwardly as is the case with coniferous trees, and the 

 analogy therefore fails. A severe winter causes great mor- 

 tality among those which are laid in pares or shore-beds, 

 in consequence of the valves being closed by ice during 

 the recess of the tide. In all probability the stock of sea- 

 water, which had been taken in before the oyster was laid 

 bare, requires occasional aeration from the atmosphere. 

 The green colour, so much prized by the Parisians, is 

 owing to the oyster feeding on the Navicula, a kind of 

 Diatom or vegetable organism which abounds in compara- 

 tively still and brackish waters. According to physiolo- 

 gists, the intestine passes the heart without coming into 

 contact with it, being an exception to the general rule with 

 respect to the relative position of these organs in the 

 Acephala. The oyster, therefore, cannot in fairness be 

 twitted with the proverb that the way to the heart is 

 through the stomach. Nor is the idea of its being 

 " crossed in love" less fallacious, seeing that each indi- 

 vidual is of both sexes, and can only be enamoured of 

 itself. 



Clark, as well as Sowerby, asserts that the animal has 

 two adductor muscles, and that the corresponding impres- 

 sions may be seen in each valve, the posterior one being 

 .very small and placed close to the hinge. I have not been 

 able, however, to detect more than one impression, which 

 lies nearly in the middle. I would therefore invite the 



