ENLARGEMENT OF PARTS FROM USE. 31 
remarks: “It seems extraordinary and beyond belief 
that the A/eleagrina should, of all the Conchifera, be the 
one to resent the commensalism of the Pea-crab, which 
has been known since the days of Cicero, Pliny, Oppian, 
and Aristotle to inhabit the shell of the Pinna and the 
Oyster, and has been recorded from Astarte, Pectunculus, 
and at least some half-dozen other bivalves, with whom 
it appears to live on the most friendly terms. It is the 
females, however, which constantly reside within the 
shells of the Conchifera, whilst the males are said to 
avail themselves of favourable opportunities to visit the 
females in their retirement.” 
Whether or not the unlucky male in this case in- 
truded himself upon Meleagrina at an unfavourable 
period, and, finding no female Pzxnotheres, penetrated 
so far beneath the mantle of the pearl-mussel as to be 
unable to retreat, one thing is quite clear, namely, that 
Meleagrina entombed the intruder in a cyst of pearl, 
from which the clever pearl-button maker alone liberated 
him. 
Increased thickness of the shell of an oyster from 
irritation is comparable to the formation of thick skin 
under similar conditions. The thin shells of “ native 
oysters” living in quiet shallow water stand in striking 
contrast to the huge, rough, laminated shell of the 
“North Sea oyster” which has to contend with the 
pressure of a large volume of water and much buffeting 
from a tumultuous ocean. So that a native oyster, when 
compared with one from the North Sea, resembles the 
hand of a courtier when contrasted with that of a 
peasant. 
