CONFERENCE OF GOVERNORS. 65 



a ciliated external projection appears, a more or less permanent 

 organ of locomotion, the foot. In the later development the foot 

 comes to contain one or more loops of the intestine, the reproductive 

 glands, one of the three " brains," the so-called " ear," muscles, 

 nerves, and a gland comparable in some degree functionally to 

 the spinning gland of the spider, since by means of this gland the 

 young clam and scallop spin threads which fasten the animal tem- 

 porarily to stones, sticks, seaweed or other sub-strata. The oyster, 

 however, is fastened in permanent fashion by the shell, and does 

 not voluntarily change position, as do the clams, quahaugs and 

 scallops. All these animals by growth add successive layers to the 

 margins of the shell, so that the concentric lines of growth may 

 indicate in general the rate of growth and the age of the individual 

 mollusk. The rate of growth is largely conditioned by the quantity 

 of food available, by the period of submergence during which feed- 

 ing is possible, by the currents, the temperature of the water, and 

 doubtless to some extent by individual personal equation. 



According to these factors, the rates of growth vary enormously 

 under various conditions, and even in rare instances attained 1,800 

 per cent, increase in volume in one year. But the usual gains 

 are from 200 to 800 per cent, for the first year, each succeeding 

 year being approximately one-half of the gain the previous year, 

 under identical conditions. Molluscan old age approaches after 

 five to eight years, though under unusual circumstances oysters 

 and quahaugs appear to have survived fifteen or eighteen winters. 

 The scallop, however, is a notable exception. Our observations in- 

 dicate that the scallop breeds when one year old, and less than 

 twenty-five per cent. "of the individuals survive in nature to reach 

 the second spawning period. Thus we see that, since the scallop 

 is naturally a decadent species, singularly exposed to dangers from 

 enemies and inclement weather, and since each individual during 

 its life produces but a single litter of eggs, the destruction by 

 man of any considerable quantity of scallops previous to this 

 spawning period can mean nothing less than commercial exter- 

 mination, possibly followed by ultimate and absolute extinction 

 of the species. 



The young clam or scallop may remain attached to its sub- 

 stratum by threads for several days or even weeks. But ultimately 

 the clams drop ofE and burrow into the sand or sandy mud; while 

 the scallop drops upon the sea bottom, over which it compasses 

 spasmodic and indefimite locomotion by violently clapping its 

 shells. Innumerable millions of young moUusks of microscopic 



