16 THE POPULAR SCIENCE MONTHLY. 



its proper place the invisible cement. The precise method of the oper- 

 ation is not, I think, understood. It seems to me that the process is 

 not a direct one, but rather the result of another process. All can 

 recollect the once-popular mackintosh, a sort of water-proof cloak. It 

 was little else tlian ordinary cloth, with an insoluble substance infused 

 into the spaces between the fibres of the fabric. Is it not likely that 

 the oyster has a process of its own not very dissimilar ? that it de- 

 posits a delicate net-work of animal substance as the staple, and that 

 this is soon filled in with carbonate of lime, taken in mechanically 

 from the salt-water ? And this same organ has, along its edge, a se- 

 ries of pigment-cells, from which it exudes the paint that decorates the 

 shell. In this respect the American oyster is a very plain affair. That 

 of Europe has more color on the shell, I think, as it is more corrugated 

 in form, and of less size. Our own oysters, we believe, both in quality 

 and size, excel all others. (For a group of European oysters, of ages 

 varying from that of three days to that of one year, see Fig. 2.) 



If the shell of an adult oyster be examined, it will appear to be a 

 series of shells, lying or lapping upon each other like tiles. There is, 

 however, a difference. The lap of the upper one is not merely on the 

 upper end of the lower one, but also on the middle, thus leaving a 

 margin nearly all round. So the uppermost layer is always the 

 smallest, and the lowermost one is always the largest of the series. 

 The oystermen call these laps " shoots " each one represents a sea- 

 son's growth. Thus each " shoot " shows the precise size of the oyster 

 at a given year of its life, while the sum of the entire series gives the 

 exact number of years the creature has lived. This shows how often 

 the logic of Nature runs in parallel lines ; for it brings up the old 

 maxim again, " Every one to his own trade." The botanist counts 

 the season-rings in the bole of a tree. The jockey tells the age of 

 the horse by its teeth. The drover sets down the age of the cattle he 

 buys by counting the rings on the horns ; and in like manner the oys- 

 terman comes to a judgment by the number of "shoots" on the bi- 

 valve's shell. But all these specialists alike err when giving judgment 

 upon an individual that has reached extreme old age. 



The capability of the univalve mollusks to repair the shell when 

 broken has been long known and understood by naturalists. In re- 

 spect to the bivalves not so much is known. The oyster has some won- 

 derful things in the way of repairing its house after being broken into. 

 A case is known to us in which an oyster was so badly fractured at 

 the nib that a piece of shell about an inch wide was broken off, and 

 the poor animal pi-otruded. An oysterman, for experiment's sake, 

 restored it to the water, and, to be sure, put it close by a pole driven 

 into the bed. This was in the spring. In September it was taken up 

 and examined, when lo ! the ingenious little builder had thoroughly 

 repaired all damages ! 



The Nervous System of an Oyster. Physically unstrung, the 



