94 
THE PEARL OYSTEK 
direct their own course in accordance with their instincts. 
But whether this be so or not, and whether the currents are 
also factors in their distribution, it is well to note that 
Franklin's Chart of 183S-1845 says of the Gulf of Manaar 
" the current is generally with the wind, but in May and 
October becomes very variable," and May we have seen is 
one of the spawning months, so that variety of superficial 
current, if a factor, would account for widened distribution. 
So far then, or while in the larval form, there would 
seem to be no marked difference in the habits of the young of 
the edible and of the pearl oyster. It is from the time that 
they are precipitated as spat that the difference commences, 
the pearl oyster having migratory powers, as we shall see in 
connection with its foot, its byssus, and its shell. 
The Foot. 
The edible oyster, from the time when it is precipitated 
as spat, is immovably cemented for life to rock, if it chance 
to fall on rock, or if it fall on mud, lies, by its weight, help- 
lessly on its heavy convex side ; and in consequence of our 
pearl bearer having been commonly called an oyster, the 
mind is prepared to expect the same of it, but it has a 
locomotive organ in what must be called a foot, like that of 
the gastropods, with which it walks with ease. Eemember- 
ing that our pearl bearer [Aricula {meleagrina) fucata] is a 
mussel, we note, in Tryon's Structural and Systematical 
Conehology, that like movement has been recorded by Dr. 
Lockwood of an American marine mussel, Modiola jylicatiila, 
which, " when placed in an uncongenial position, can use 
its foot in escaping with as much facility and in the same 
manner as a gastropod, not only traversing a part of the 
bottom of his aquarium, but actually gliding up its per- 
pendicular wall to a distance of six inches," and " the river 
mussel di'ags itself slowly along by protruding and contract- 
ing its flexible foot." But we have to do ■with an animal 
