50 ANIMAL PAEASITES AND MESSMATES. 



also develop themselves on the eggs of the Plagiostoma, 

 and are then capable of living separately. In the sub- 

 stance of this polyp lives a crustacean, the nature 

 of which Mons. Lacaze-Duthiers has not yet made 

 known. 



The superb sponge, Euplectella aspergillwn, the 

 elegant structure of which cannot be sufficiently ad- 

 mired, is, unlike the Alcyonium of the Dromia, rooted to 

 the soil, but nevertheless gives shelter to three kinds of 

 crustaceans : Pinnotheres, Palemonidas, and Isopods. 

 These supposed plants have been known for many years 

 under the Spanish name of Regadera, or the English 

 "Venus' Flower-basket;" they were first brought from 

 Japan, and afterwards from the Moluccas, and more 

 recently from the Philippine Islands. In almost all the 

 individuals which Professor Semper was able to study in 

 those parts, were found the same crustaceans. These 

 Euplectellse have just been met with to the south-west of 

 Cape St. Vincent, by Wyville Thomson, who has brought 

 up some from a depth of. 1090 fathoms, while on board 

 the Challenger. This skilful professor has discovered 

 another sponge to the north-west of Scotland, at a 

 depth of 460 fathoms; it bears the name of Holtenia 

 Caiyenteri; and I have in my possession a fine specimen 

 which I owe to his generosity, and keep as a souvenir of 

 the delightful hospitality which he extended to me at 

 the Edinburgh meeting. 



There are also sponges which construct a dwelling 

 in the abode of their neighbour. We find, among others, 

 a small sponge known under the name of Clione, which 

 establishes itself in the substance of the shell of oysters, 

 and hollows out galleries as the teredo does in wood. 



