258 



LOWER INVERTEBRATES. 



cotta which measured fifteen inches in length. Remains of other beds, and indications 

 of still others in the shape of kjokkenmoddings, are abundant along the coast, at Port- 

 land, Harpswell, and points in Massachusetts. 



It seems that most of these beds, north of Cape Cod, have become extinct since 

 the first settlement of the country. The old records tell of beds in the Mystic and 

 the Charles Rivers, near Boston, which were well known to the early settlers, but all 

 trace of them is now lost. The same is true of many other places. What was the 

 cause of this extinction is not easy to decide. Professor Verrill, who has taken into 

 consideration the facts afforded by the past and present distribution of other mol- 

 luscs, is inclined to attribute it to :i climatic change ; others to over-fishing, pollution 

 of the waters, etc. 



South of Cape Cod the oyster still flourishes in its native vigor, and an enumera- 

 tion of the places with extensive beds would be about equivalent to giving a catalogue 

 of the shore towns from Buzzard's Bay to Texas. In Long Island Sound, and on the 

 Jersey coast, besides the supply of natives, large numbers are transported from the 

 Chesapeake. These latter are brought in the shape of small (seed) oysters, and are 

 scattered in suitable situations, where they increase in size. When large they are 

 taken up and sent to the market. The profits on this operation are said to be large. 

 It is in Chesapeake Bay, and its various creeks and sounds, that the oyster business 

 reaches its greatest development, and where the study of the various economic and 

 scientific problems connected thei'ewith, have received the greatest attention, an 

 account of which will not be out of place here. 



In our American oyster the sexes are separate, and, thanks to the labors of Dr. W. 

 K. Brooks and Mr. J. A. Ryder, we now have a pretty 

 complete knowledge of the life history of this valuable 

 form. The eggs are fertilized after leaving the parent, 

 and undergo their development in the water. The de- 

 velopment is normal and direct. After the formation of 

 the velum the young oyster swims freely through the 

 water, during which time the shell and the internal 

 organs are being gradually developed. In a few days 

 this free life ceases, and the young oyster attaches itself 

 to some submerged object. The way in which attach- 

 ment is effected is at first by the rudimentary shell of 

 the left valve, and subsequently, as lime salts are de- 

 posited in the shell, they serve to unite the young oyster 

 more firmly to the point of support. When first attached, the young oysters are 

 termed 'spat ; ' when large enough for transjslanting, ' seed.' 



The life of the oyster depends ui^ou many things, tlie most prominent being the 

 location. At the time the embryos are to be converted into spat they need some solid 

 object to which to attach themselves. On the natural beds this is found on the shells 

 of other oysters and on rocks, but where artificial beds are formed it is customary to 

 throw down old shells. In artificial propagation 'collectors' of earthenware, slate, etc., 

 are used. The young oyster needs plenty of water and food, and also needs protection 

 from mud, which would soon smother them. The food consists almost wholly of mi- 

 croscopic animals and plants. 



Many experiments have been tried to raise oysters in confinement, but until recently 

 they have not been successful. The great trouble has been in keeping the young alive. 



Fig. 267. — Young oyster. 



