18 NEW YORK STATE MUSEUM 



Methods 



Each clam was measured in sixteenths of an inch at the time of 

 planting, and also when taken from the bottom six months after- 

 ward. Merely to state the increase in length, however, gives no 

 adequate idea of the actual growth. It is much better to give the 

 increase in volume. To state that a clam increases from 

 i-ftf to i |f inches in a certain time gives little idea of its actual 

 growth. If individuals of the two sizes are held in the hand and 

 compared by the eye, the bulk of one is seen to be much greater 

 than that of the other. It is really this increase in volume which 

 we wish to determine, so each clam was measured also by deter- 

 mining its displacement in water. A table was made showing the 

 displacement of clams of various sizes. For example, many indi- 

 viduals just I inch in length were measured in a graduated vessel. 

 There is some slight variation, because some are thicker than 

 others. The average of many measurements, however, show that 

 a clam of this length displaces 2.5 c.cm. The average displace- 

 ment of other sizes was determined in the same way. 



To illustrate the difference in the two ways of stating the increase, 

 we may compare clams I and 2 inches in length. One is 100$ 

 longer than the other. One has a volume of 2.5 c.cm, the other a 

 volume of 22 c.cm; and, while a clam I inch long has increased in 

 length 100$, it has increased in bulk or volume 780$. This increase 

 in size or volume is what we wish to determine. 



Suppose that in a certain bed are placed clams all of a size. 

 When these are dug, after a lapse of several months, some indi- 

 viduals will have increased in size more than others, though the 

 differences may not be great. In order to determine the increase 

 in such a bed, the arithmetical mean length of the whole series 

 has been calculated, and the volume of the mean has been com- 

 pared with the volume of the clams when planted. 



In one bed, for example, several clams i T 3 5 inches in length were 

 planted. In six months they were removed, and the length of each 

 individual carefully measured. There was some individual variation 

 in the length; so the mean length of the series was calculated. It 

 was found to be i-i| inches. The average volume of clams I T 3 ^ 

 inches long is 4.5 c.cm; that of individuals i-}f inches long is 



