CRABS — PARASITES. 2.-53 



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 coidd 

 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 Pinnotheres 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 pinna Augnst!mSL 



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 pisurn). 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 ? 



