MARINE WORMS, 37 



The various species named have been brought together 

 by no single cause but by several interacting interests of which 

 I shall now proceed to attempt the explanation : — The rougher 

 a rock surface be the better shelter will it naturally afford to 

 weak and defenceless animals ; thus the bright green 

 worm Eulalia viridis, on a lime-stone coast, where the 

 rocks and boulders are perfectly honeycombed by erosion, 

 is found in wonderful profusion, while on an adjacent one of 

 smooth surfaced schist or slate it is all but absent. Now the 

 Ascidian-coated rocks of our district are almost a parallel in 

 roughness to a much eroded limestone surface, there being 

 every grade of size among the Ascidians, from an eighth to 

 one inch in height. The Ascidian colony once started is a 

 nucleus around which much diverse life gathers. Spores of 

 algae settle and grow ; minute crustaceans gather round, am- 

 phipods, isopods, pycnogons ; first one worm and then another 

 takes up lodging between and among the Ascidians, and with 

 the growth of the colony, the tubes first constructed become 

 covered and protected, for Styelopsis seems to be left severely 

 alone by all manner of beasts. I have never seen sign of it 

 being browsed upon. 



As to food, this strange assemblage of animals may be 

 said to be self-supporting. The Ascidians, by means of their 

 inhalent currents, gain possession of minute life — diatoms and 

 the like — from the surrounding water ; the crustaceans feed 

 upon faecal matter, algae and minute animal life, and the worms 

 upon the Crustacea, f orams, and diatoms that abound. 



The final instance which I shall give is perhaps the most 

 interesting of all, as hitherto it has been undescribed. My 

 acquaintance with it dates indeed only from the 8th Novem- 

 ber, 1892, when, being out collecting at extreme low water 

 mark at the Greve d'Azette, Jersey, my attention was 

 attracted to several large patches of a crusting orange-red 

 sponge on account of the peculiarly emphathic markings of 

 what appeared to be the oscula. Being suspiciously unlike any- 

 thing spongiform, I secured some good sized pieces of the 

 sponge for microscopical examination at home. Sections 

 proved them to belong to the Mlcrociona plumosa of Bower- 

 bank (" British Spongiadae," Vol. III., page 61), but the 

 supposed oscula which, to the naked eye, appeared as 

 innumerable tiny black specks, each surrounded by a grey 

 circle, turned out to be in reality the ends of tubes tenanted 

 by an eyeless species of Leucodore (L. cceca, CErsted). 

 Within the space of a square inch upwards of forty could 

 frequently be discerned. 



