598 
BULLETIN OF THE BUREAU OF FISHERIES 
working with small, juvenile scallops, found that it occurred if one of these was ap- 
proached ventrally with the point of a pencil and evidently was for the purpose of 
taking the scallop away from the pencil. Anthony, Buddenbrock, and Uexkiill 
attributed this movement to a direct local stimulus. Dakin found the cause in 
sudden stimulation. I have observed this “backward” darting, especially when a 
scallop was touched suddenly, but, working with mature or nearly mature individuals 
kept in captivity, have not been able to induce it at will by mechanical stimulation. 
It seems to be in part a startled movement but I have induced it by repeated chemical 
stimulation of the midventral portion of the mantle margin. 
According to Dakin and Buddenbrock this reversal in direction of progression 
is due to an indrawing of the velar fold during shell closing, according to Anthony and 
Uexkiill to a local contraction of this structure which is so important for swimming. 
If this latter explanation is correct it is strange that the darting, according to all 
these accounts and in so far as I have noticed, is always hinge foremost and not 
sometimes hinge sidewise or diagonally. 
A third type of movement described by various investigators (for example Dakin, 
Buddenbrock, and Uexkiill) is that by which a scallop turns over after being placed 
wrong side up. This is performed by arranging the velar folds, along the ventral 
margin of the shell, so that when the valves are forcibly brought together, a stream 
of water is directed downward against the bottom. This lifts that edge of the shell 
and turns the scallop right side down. Belding (1910) states that the turning ordi- 
narily is forward or backward. With local, adult specimens the turning is somewhat 
difficult to study, for scallops so placed (contrary to the experience of Grave (1909)) 
may remain wrong side up for hours, and indeed have been found, although rarely, in 
this position on the flats. It seems probable that scallops of this species lie so nearly 
universally in the normal position principally because they settle on the right side 
after swimming, which is with the left side up. As previously noted, Buddenbrock 
(1915) foimd that Pecten may also right itself around an axis perpendicular to the 
hinge line. 
Jackson (1890) described a sort of “scuttling” movement over the bottom pro- 
duced by repeatedly expelling water through one velar gap only. 
Anthony (1906) noted that a scallop may rotate horizontally by a single, mod- 
erate contraction which drives the water between the velar folds at one point only. 
Although scallops have been supposed to shift considerably and even to make 
distinct migrations, field observations indicate that during a large portion of the 
scallop’s life shifting ordinarily, in local waters, is very slight. Not only do near-by 
flats yield scallops of different size or shape but, in some instances, different portions 
of a large flat yield scallops notably different in size. Thus, in western Bogue Sound, 
scallops of good size were found along the edge of the dredged channel north of 
Lovetts marsh. A few rods away from the channel scallops were of the dimunitive 
size usual in this section of the sound. Other instances have been noted. Indeed it 
seems probable that shifting, except as the vegetation to which the young scallops 
cling becomes detached^ and is carried away by wind or tide, is slight after the veliger 
stage is passed. 
