CRABS — PARASITES. ; 253 
species, which disguised itself by investing its body with a 
covering of decayed vegetable substances and coral-sand. The 
better to ensnare its prey, the back was covered with rigid and 
incurved bristles, calculated to retain the extraneous sub- 
stances, while the short and well concealed forceps-claws were 
ready for the attack, and the ophthalmic peduncles, curving up- 
ward to raise the eyes above the pile of materials, gave the wily 
crab the great advantage of seeing without being seen. As soon 
as an unfortunate mollusk, unsuspicious of evil, approached the 
lurking ruffian, he darted upon it like an arrow, and, ere it could 
recover its presence of mind, was busy tearing it to pieces. 
If many crabs are burdened with small animals and plants, 
others live parasitically in the shells of mollusks. Thus the 
small Pivnotheres veterum claims the hospi- 
tality of the Pinna, a large bivalve of the 
Mediterranean. The ancients supposed that this 
was a friendly connection, an entente cordiale, 
formed for mutual defence: that the Pinna, 
being destitute of eyes, and thus exposed when Pea-Crab. 
he opened his shell to the attacks of the cuttle- _ 
fish and other enemies, was warned of their approach by his 
little lodger, upon which he immediately closed: his shell and 
both were safe. Unfortunately, there 
is not a word of truth in the whole 
story. The sole reason why the Pin- 
notheres takes up its abode under a 
stranger’s roof is the softness of its 
own integuments, which otherwise 
would leave it utterly defenceless; nor does the Pinna show the 
least sign of affection for its guest, who, on returning from an 
excursion, often finds it very difficult to slip again into the 
shell. 
According to Mr. Thompson, the Modiola vulgaris, a species 
of mussel very common on the Irish coast, almost always har- 
bours several parasitic crabs (Pinnotheres pisum). At Heligo- 
land, Dr. Oetker, to whom we are indebted for the best work 
on that interesting island, scarce ever found a modiola without 
several guests of this description, while he never could find any 
in oysters, mussels, and other nearly related species. What may 
the reason be of either this predilection or that desertion ? 
Pinna Augustana, 
