340 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
examine the very young stages of P. maaimus, but P. 
opercularis and P. wrradians of the American coast have a 
period before the free stage is reached, when they attach 
themselves by means of a byssus. 
In a still earlier stage after the free-swimming larva 
has settled down, the animals are unattached and crawl 
about actively. The foot is protruded, attached to some 
object and then contracted, and in this way the animal 
is pulled along by successive attachments and contractions 
of the foot. The foot of the adult Pecten is very like a 
sucker, though in no case have I seen it used in the 
manner above described. 
Following the crawling stage we have the byssus 
stage, and the foot takes part in the attachment of the 
threads. 
Jackson (8), who has watched the American species, 
describes it as follows :—‘* Lying on the right valve, the 
foot is extended on the surface of the dish, the flattened 
distal portion taking a firm hold as if about to crawl. 
This position is maintained for a moment or two and then 
the foot is withdrawn within the body, by the motion of 
retraction 1t draws out, or spins, the byssal thread, which 
the creature had fixed to the surface of the dish while the 
foot was laid closely against it. Soon the foot is again 
extended, pressed flatly against the dish and another 
byssal thread is spun, three is the common number with 
specimens in confinement.” 
If disturbed the attached scallop can break or 
cast off its byssal threads and swim by clapping its shell. 
The adult P. opercularis only occasionally shows any signs 
of the byssus, but P. varius, another common British 
species, is usually attached. 
Pecten feeds largely on yegetable matter, such as 
diatoms, fragments and spores of algae, together with the 
