38 MARINE WORMS. 



The conclusion I come to, after examination of a large 

 number of specimens, is that actual benefit is mutually given 

 and received by each of the two messmates. The sponge 

 certainly gains considerable support and extra consistency from 

 the comparatively numerous wiry upright tubes of the annelid 

 ■ — and there is also the question whether the excreta of the 

 worms is of any food value to the sponge. On the part of the 

 commensal worm there is little doubt that it finds a valuable 

 protector in the sponge, which, it is noteworthy of mention, is 

 characterised by an intensely rank smell of garlic (warning 

 odour ?). As I have seen no sign of the sponge host being 

 preyed upon by any animal, we may conclude that its pro- 

 tective devices of spicules, odour and taste, are fairly successful. 

 A worm whose tube is sunk completely in its substance will 

 naturally be very safely housed, and besides, the friendly 

 water currents set in motion by the sponge cilia will bring 

 much food matter to its very mouth. 



Bowerbank, in his description ("Br. Sp. Vol. II., p. 134), 

 writes of a specimen as "permeated by some small tubular 

 zoophyte which it has coated with its own tissues, and from 

 these adopted columns defensive spicula are projected," — 

 evidently referring to the same thing as I describe above — 

 but mistaking the tube formed as zoophyte instead of annelid. 

 Evidently from this mention the habit must be somewhat 

 widely spread. 



There cannot fail to be many further instances of this 

 interesting inter-relationship between animals yet to be 

 recorded. The study well repays any time devoted to it ; 

 little preliminary zoological knowledge is required — an ordi- 

 nary text book of zoology being ample provision to make — 

 and not the least of its advantages is that it is necessary to 

 carry out the research in " the free air and light of heaven," 

 a briny breeze fanning one's cheeks as one turns over the 

 trailing brown weeds festooning and draping caves, chinks and 

 gullies in that richly peopled strip of shore that uncovers but 

 a few times a year on the occasions of the lowest spring tides. 



Note. — In dredging in deep water off the Isle of Man, 

 I have often found a Nereid (Nereis fncata) as a common 

 commensal with the Hermit Crab in old Whelk Shells. Here 

 I have never met with it, so if any member should encounter 

 any when dredging, as also the Polynoe commensal (A. 

 astericola), in the ambulacral groove of Astropecten, I shall be 

 much indebted if they be preserved in spirit and sent to me. 

 Nov. llth, 1892. James Hornell. 



