OF THE GULP OF MANAAR. 97 
held its foot-hold firmly, and without any byssiis, till I 
forcibly pushed it down with the fork. Then in falling, 
free of the side of the tumbler, it made some effort by 
which it regained the side of the tumbler before it had fallen 
half-way, and immediately resumed its walking ascent till 
it reached the surface. I forcibly dislodged it three times, 
always with the same results — a quick movement to the side, 
and an immediate march to the surface. When I left it in 
peace at the surface, it began to feed off its own shell-borne 
commissariat, of which more hereafter, forcibly ejecting what 
was passed or ejected, but still without a hyssus. During the 
two hours of obseryations no byssus was thrown out, and early 
the next morning I noticed that still no byssus had been 
formed by oyster No. 1 ; oyster No. 2, which was attached 
by its byssus to the shell of No. 1 while these observa- 
tions were being made over-night, and which had then been 
striving in vain to reach the glass with its foot, having at 
length succeeded, in the course of the night, in gaining it, 
and thereon marched upwards till it got its own umbo level 
with the surface, and that of No. 1 clear out in the air, and 
so No. 1 was by the byssus of No. 2 held in a position in 
which neither its foot nor byssus could reach the glass. It 
was very clear to my mind that the animal used its foot, and 
its foot only for walking, and also for being temporarily 
stationary, and that the byssits was not put forth till the 
animal had reached a position in which it was content to 
stay more than temporarily. The foot, too, seemed to be 
capable of being used as a natatory organ, in which it is 
again like the heteropods or swimming gastropods (water- 
snails). In this connection I may mention in passing that 
I noticed a round opening in the sole of the foot, and im- 
mediately anterior to the mesopodium which is said to be 
the opening of the pedal aqueous system common to many 
gastropods. No. 2 was the smaller pearl oyster of the two, 
