344 OUT Food Mollusks 



may reach the grass blades above the bottom, for they 

 still continue to swim from time to time by the paddling 

 motion of the foot, and then by the shell, and during 

 these short journeys they may attach on striking any 

 solid body. They may perhaps also attain a lodgment 

 above the bottom by creeping up the grass blades, and 

 this is a function of the foot not yet described. 



When the small scallop settles, on the disappearance of 

 the velum, the foot is relatively of great size, covering the 

 entire ventral surface of the body. Frequently the ani- 

 mal extends it, attaching the end by a sucker-like action ; 

 then by a contraction of the foot, the body is drawn 

 toward this point, and by a repetition of the process the 

 young Pecten creeps and often climbs up vertical sur- 

 faces. This habit is continued for some time, and dur- 

 ing the creeping period, of course, swimming and byssus 

 attachment are also practised. 



It is interesting to observe that Pecten as well as Mya 

 and Venus, and probably other bivalves, possess what 

 may be called the creeping stage, a definite period during 

 which they employ a part of the time in creeping on 

 the ventral surface of the foot, and for the remainder lie 

 attached to various objects by means of a byssus, which 

 they may cast off and reform at will, and also, in the case 

 of Pecten, in swimming. In 1891 incidental mention 

 in papers published by two German biologists was made 

 of the fact that the young of the bivalve Dreissensia ex- 

 hibited the habit, after the swimming stage and before 

 attachment, of creeping on the bottom. Details of this 

 curious habit, however, were first published by the writer 

 from observations made on the soft clam Mya, and re- 

 cently it has been studied more thoroughly in Pecten 

 and Venus by Mr. Belding. As the habit of creeping 



