3478 



CCELENTERA TES 



unattractive when in spirit, are of a sulphur yellow, and beautiful when alive in an 

 extended condition. The most interesting species is Palythoa fatua, which is 

 always found growing on and in one of the most curious of sponges, the Japanese 

 glass-sponge (Hyalonema) . Here the surface of the stalk, that is above the portion 

 embedded in the mud, is covered with a warty crust belonging to this Palythoa. All 

 the specimens of this Japanese sponge in European museums in 1860 had their 

 stalks overgrown with the Palythoa, while many had their bodies also covered with 

 another polyp which, however, settled singly and, fortunately for the sponge, did 

 not form a sandy crust. The illustration represents a specimen of this beautiful 

 glass-rope sponge, its body pitted all over with holes in which small Anthozoa 

 once lived, and its stalk coated with the sandy crust of the stock-forming 

 Palythoa. The former, having no skeleton, dry up entirely; no traces of them 

 being found in dried specimens of the sponge except the holes they lived 

 in. Unlike a parasite, the polyps do not feed upon the juices and soft parts of the 

 sponge, nor indeed do they share its food, but simply settle upon the sponge and feed 

 upon the food that may chance to come within reach. It is interesting to note that 

 a Palythoa closely related to the Japanese form occurs in the Adriatic, and is also 

 attached to sponges, scarcely a single specimen of the sponge in question being 

 found without its polyp guest. The larvae hatched from the eggs of the Palythoa 

 evidently perish unless they meet with one of these sponges; but the manner in 

 which they find and recognize their particular host is quite unknown. Other species 

 of Palythoa found on the American coast settle on the shells inhabited by hermit 



crabs, covering the shell as an uninterrupted mass several 

 lines thick, and the individual polyps rising to about an 

 equal height above the general mass. The shell becomes 

 disintegrated beneath this cover, and the polyp stock then 

 remains as the only covering to the crab. In this case there 

 is mutual advantage, for the crab is covered and protected 

 by the polyp stock, while the polyp profits by its wander- 

 ings and enjoys constant change of water and new fields 

 for food. 



An extraordinary form, very nearly allied to Zoan- 

 tharia, has been described under the name of Polyparium 

 ambulans, and is found in the strait dividing the island 

 of Mindanao from that of Billiton. It consists of a colony 

 three inches long and six wide, flattened from above down- 

 ward, and therefore more or less ribbon-like; and the 

 anterior cannot be distinguished from the posterior end. 

 The upper surface of the colony is covered with peculiar 

 polyps shaped like chimneys, the base being much wider 



than the top; which carries a round aperture. Each polyp 

 Palythoa axinellce (some- 

 what less than natural * s extremely minute, and has no tentacles. They stand 



size). in irregular transverse rows of from five to eight, differing 



The small dried-up polyps are j n a g e an d therefore in size; the lower side, on which the 



seen adhering in groups to 



the branching sponge. colony rests, being beset with protuberant suckers. These 



