The Scallops 345 



seems to be of little or no value to any of these forms, 

 except possibly to Pecten, and as the foot in all of them 

 is at this stage proportionately a very large organ, 

 though later becoming greatly reduced in Mya and Pec- 

 ten, it may be assumed that the adult ancestral form of 

 each possessed a large foot capable of effecting relatively 

 long journeys, and that the creeping habit here exhibited 

 by the young of their modern descendants is merely a 

 memory of that ancient practice. Venus still retains the 

 large foot in the adult condition, but in the light of the 

 experiments mentioned in the previous chapter, seems, 

 after it has begun to burrow, to make little or perhaps 

 no use of it in locomotion. 



On account of the depth of water in which it lives, the 

 early period in the life of the giant scallop is unknown. 

 The adult seems not to be able to attach itself, though 

 there is a byssus gland in the foot ; but there are no rea- 

 sons for doubting that the young has the same habits of 

 creeping and attachment that are found in its smaller 

 relative. 



Some of the facts concerning the growth of Pecten ir- 

 radians are of great interest and economic importance. 

 Increase in size, after the scallop has settled from its em- 

 bryonic swimming state, is fast or slow according as 

 food-bearing currents are favorable or not ; but growth is 

 most rapid in August and September, and decreases 

 steadily as the water becomes colder. When, about the 

 first of December, in New England south of Cape Cod, it 

 has reached 50 F., growth ceases altogether. It is only 

 resumed when, about the first of May, the temperature 

 again rises above that point. It thus appears that in New 

 England there are five months in the year when the scal- 

 lop does not grow. The same is true of the hard clam, 



