1020 ON A NEW INSTANCE OF SYMBIOSIS, 



in which one animal finds it advantageous to take up its abode in 

 the walls of the dwelling of another. But here we have something 

 more. The tube in which the Anemone dwells is not formed by 

 the Anemone alone, but is partly manufactured by the Phoronis. 

 This is proved by an examination of the texture of the tube, which 

 is partly made up of gelatinous threads containing a large amount 

 of the same dark purple pigment found in the integument of the 

 tentacles and front part of the body of the Phoronis, and partly of 

 much finer threads. 



Among the meshes of the latter, which form the greater part 

 of the thickness of the tube are numerous oval thread-cells, and 

 the thick felt-like substance seems to consist of nothing else than 

 the discharged flagella of these bodies (1). The Phorones inhabit 

 transparent membranaceous tubes which run obliquely in the 

 substance of the tube of the Cerianthus, projecting usually a little 

 distance beyond the general outer surface of the latter— the mouth 

 directed more or less upwards. The openings of thesa smaller 

 tubes lie over the whole surface of the large tube ; except a short 

 .space at the lower end, the tubes themselves form a substantial 

 part of the thickness of the latter, and there can be little doubt 

 from the way in which the threads which seem to be derived from 

 the Phoronis are interwoven with those produced by the thread- 

 cells of the Cerianthus, and from the intimate manner in which 

 the smaller tubes are interwoven with the tissues of the larger one 

 that the two structures — the colony of Phoronis and the pro- 

 tecting case of the sea-anemone — have grown simultaneously. 



The symbiosis of a Sagartia with a Pagurus has been described 

 by Eisig — the hermit-crab permitting the sea-anemone to live on 

 the back of its shell, and the sea-anemone apparently preferring 

 this situation to any other (2). The advantage derived from 

 association with one of the Actinidce in all such cases, is 



(1). Thread-cells of similar shape occur (with others) in the ectoderm 

 ot the body wall of the Cerianthus, though not of the tentacles, the 

 nematocysts of the latter being all along and narrow with a spiral thread. 



(•J). Dromia excavata. another of the Anomoura, found in Port Jackson, 

 is almost always found with a colony of Diazona, a solid heavy compound 

 Asoidian, growing on its back — the Diazona frequently being very many 

 times the bulk and weight of the Crustacean. 



