56 THE SCALLOP FISHERY 



and crawling by means of the foot with its ciliated tip; (2) the true 

 crawling stage, where locomotion is by means of the foot ; this is found 

 only in the early dissoconch scallop and is of short duration; (3) crawl- 

 ing with the foot and swimming by a clapping of the valves, as in the 

 adult. The actual use of the foot for crawling covers a long period, 

 as the animal continues to creep more or less until it reaches a size of 

 iy inches, when the foot becomes too small for this purpose. 



Climbing. Climbing rather than horizontal crawling seems to be 

 the natural instinct of the young scallop, which seems to prefer going 

 up the sides of an aquarium to crawling over the bottom. Young scal- 

 lops 0.6 to 0.8 of a millimeter, placed in a glass dish, climb up the sides 

 until they find a place for attachment by the byssus, crawling over or 

 around obstacles with equal readiness. A needle was placed before a 

 crawling scallop, and it climbed up this for several millimeters before it 

 found a resting place. The usual point of attachment is just below the 

 surface, but the scallop may encase itself in a drop of water somewhat 

 above this level. The scallops do not climb out of the water, as evi- 

 dently the siphon helps the foot in the work of climbing and it is 

 impossible for the animals to lift the increased weight of the body. 



Scallops do not progress with such rapidity as in crawling, as the 

 animal is forced to support its weight when making each extension 

 of the foot. In the larger scallops the action of the foot is aided 

 by the tentacles, which at times seem to offer support as the animal 

 rests against the sides of the glass dish. The pseudo-siphon on the 

 posterior side of the mantle aids by forcing a jet of water from the 

 shell at the same time that the foot contracts. Evidently the scallop 

 maintains its position for the most part by means of the foot, which 

 makes a double bend so that a second part near the byssal gland touches 

 the surface. Possibly by using this portion as an elbow, in the same 

 manner as when the byssus is formed, it is able to cling to the support. 

 Ordinarily the lift comes directly upon the end of the foot, as scallops 

 have been observed hanging on the sides of the dish by merely the tip, 

 and to pull themselves up by the contraction of the foot alone. Part 

 of the contracted foot then rests on the glass, and the distal end lengthens 

 out, searching for another resting place. 



It was observed that 25-milJimeter (1-inch) scallops could climb 

 for a distance of 4 to 5 inches on a smooth, perpendicular surface. The 

 larger scallops were not so active as the smaller, and the 25-millimeter 

 size seems to mark the end of the climbing activity of the animal, the 

 foot evidently being unable to support the heavier body. 



The use of the climbing power is connected with the attachment of 

 the scallop. Whenever the animal is shaken from its point of location 

 it can climb back to another perch on the eel grass. There seems no 

 selection in the climbing instinct, only a tendency to mount upwards. 

 It is also possible, when the set strikes the eel grass, that the scallops 



