346 Our Food Mollusks 



and it would be interesting to know if these forms grow 

 continuously in the warm waters of the Gulf of Mexico. 

 During May growth is rapid, but in June or July, when 

 the scallop is one year old, it begins to mature and dis- 

 charge its sexual products. So great is the tax on the 

 creature's energy during the period in which it is per- 

 forming this function, that its growth is about half what 

 it had been in May. When the reproductive period is 

 passed, rapid growth is resumed. 



Actual increases in volume during known periods have 

 not been calculated, but some idea of the rate of growth 

 may be had from measurements of the longer axis of the 

 shell in successive periods. Many growth experiments, 

 carried on under varying conditions, have been made in 

 Massachusetts. They show the average length of the 

 axis of scallops spawned on July i to be about one and a 

 half inches on December i, and that on December i a 

 year later these scallops will possess a shell about two and 

 a quarter inches across. 



There have been various speculations on the normal 

 length of life of bivalves, but only in the warm water 

 scallop have we any positive knowledge of it. While 

 both of the edible Atlantic clams are known to live four 

 or five years, and probably may live longer under favor- 

 able circumstances, fishermen have generally held the be- 

 lief that the scallop's life was limited to two years, and 

 very careful observations have proved this to be true. 

 The fact was ascertained in part by observing great 

 numbers of individuals kept under normal conditions in 

 large inclosures. Many observations were also made on 

 those* living among entirely natural surroundings, and 

 altogether the data conclusively indicate a natural life 

 period of from eighteen to twenty-six months. 



