FREE MESSMATES. 21 



(lently of the Fierasfer, the Ilolothuria scahra of the 

 Philippine Islands regularly lodges in its interior a 

 couple, and sometimes, though rarely, a greater number 

 of pinnotheres belonging to t^YO distinct species. They 

 choose this domicile at an early period, and must be highly 

 delighted with this obscure abode, since they are seen 

 no more, and when they have once entered never quit 

 this living cavern. This observation is due to Professor 

 Semper, who has made us acquainted with so many 

 curious facts of the China Sea and the Pacific Ocean. 

 In the midst of the slender branches of a coral of the 

 Sandwich Islands, the Psecilopora csespitosa of Dana, 

 there lives a little crab {Hopalocarcinus marsupialiSf 

 Stimpson), which is at last completely enclosed by the 

 vegetation of the coral. It only keeps up sufl&cient 

 communication with the exterior to enable it to procm-e 

 food. The coral, however, furnishes it nothing but a 

 resting-place in the midst of its tissues. 



Among the Philippine Islands, also, a brachyurous 

 crustacean lives in the branchial cavity of one of the 

 Haliotidse, and another on the body of a holothuria. On 

 the coasts of Brazil, F. Miiller, during his abode at 

 Desterro, saw some Porcellanss inhabiting star-fish, not 

 as parasites, as had been supposed, but as true mess- 

 mates. A crustacean possessed of but little generosity 

 is the Lithoscaptus of Mons. Milne -Edwards. Provided 

 with beak and claws for the purpose of attack, it instals 

 itself, sad to say, in the pantry of a medusa, and instead 

 of making use of its own weapons, takes advantage of 

 the perfidious nematocysts of its acolyte, in order to live 

 quietly at his expense. 



Under the name of Ascllus medusa, Sir J. G. Daly ell 



