86 COMmSSION OF CONSERVATION 



height of my spat after seven days additional growth). It will be seen 

 that my spat only added in six and seven days what Jackson's would have 

 done in three and four days, 



I planned an experiment on growth through the winter by putting 

 out closed strong wire baskets containing oyster shells upon which were 

 marked specimens of minute dark spat. But these could not be found 

 next spring and I supposed that they had been tampered with — perhaps 

 by the early lobster fishing. Examination of shells off Ram Island point at 

 the beginning of June, 1905, showed some dark spat still there that had 

 apparently not grown a bit, or changed in colour during the winter. Many 

 had died and lost the upper valve or both valves, sometimes leaving a patch 

 or rim showing where a spat had been. The largest dark spat collected the 

 previous autumn measured 6 mm., and the largest now were 8 mm. in 

 height. They retained their dark metallic lustre with radiating ridges or 

 lines and very thin edges — the whole spat being thin and fitting so solidly 

 against the supporting shell as to require some force with a knife-blade to 

 separate it. In some of the larger was to be seen a tendency to turn white, 

 in that the dark rays were irregularly separated by reversed lighter radi- 

 ations. It would seem that on our coast oysters do not ordinarily grow 

 beyond these dark spat in size during the first season; that the spat growth 

 takes place during the remaining short period of warm weather after the 

 middle of August; that no growth takes place during the winter, except 

 perhaps a slight thickening of the shell. 



Winslow's experiments in Chesapeake bay showed spat caught on 

 tiles grown to f inch in 3 months. 



Ryder says that after fixation the growth of spat is very rapid — in a 

 week or ten days to J inch across, 20 days /s inch, 44 days H inch, 48 

 days 1 inch, 79 days If inches, 82 days 2 inches. 



It is possible to pick out all sizes between the little dark spat I have 

 mentioned and mature oysters of four and five inches. It is also possible 

 to arrange them into groups varying about a few definite sizes. The larger 

 specimens have characteristic concentric ridges and furrows, representing 

 periods of grow^th and rest that correspond in sizes with the smaller ones. 

 The most regular and typical of these must have reference to the annual 

 growth. I think it likely that the first deep furrow, somewhere about 1 

 inch from the umbo, marks the close of the first full year's growth — i.e., a 

 full year from the cessation of growth of the ^ inch (6 mm.) dark spat. 

 The next complete deep furrow, somewhere about 1^ to If inches from 

 the umbo, may indicate the size at the end of two full years. Another 

 furrow, about 2^ inches or a little more from the apex, three years. There 

 are secondary furrows, irregularities and perhaps exceptions, and the 

 measurements vary according as the oyster is of the long or the short 

 variety. I have not sufficiently examined this feature and have had no 



