Marine Fauna of Great Britain. 405 



frequently occur in swarms just over the muddy ground of 

 certain fishing-banks, in tlie midst of multitudes of post- 

 larval fishes which feed on them. But muddy ground is to 

 be tested as much by the forms which live in it and on it as 

 by those which, it may be, are only temporarily above it. 

 From rhizopods to fishes there is no scarcity. Dr. Murray is 

 inclined to think that " in the present period and not very 

 remote geological past " his mud-line has played an important 

 part in the spread of marine animals. Prof. Herdman, on 

 the other hand, considers that the fauna of the Laminarian 

 region is richer than that of the mud-line, and that there life 

 " is most abundant, growth most active, competition most 

 severe/' that " evolution of new forms by natural selection 

 has been most active,*' and that " migrations have taken 

 place downwards to the abysses, outwards over the surface, 

 and upwards on to the shore." Both the able naturalists just 

 mentioned have doubtless good grounds for their views, so 

 that the one theory may be as good as the other. It is 

 doubtful, however, if we are yet in a position to speak deci- 

 sively as to how and whence marine life radiated, either in 

 the present or in the past. 



Eeturning to the condition of the marine fauna on the 

 extreme west, it is found that, instead of the soberly tinted 

 sponges of the east, bright yellows and purples are met with, 

 while the firm rounded Geodia grows on stones between tide- 

 marks. The crunib-of-bread sponge, again, is partial to 

 tangle-roots and stems, while Grayitia cUiata abounds near 

 low-water mark. 



Foremost amongst the Coelenterates is the stony coral 

 {Garyophyllia Smtthii), which studs the hard gneiss stones 

 near low-water mark, especially where, piled on each other, 

 they form little caverns, in which the corals hang, grow 

 upright, or project horizontally. Equally characteristic in 

 certain creeks is Anthea cereus, which has a brownish or ash- 

 coloured body and long large tentacles of greenish and 

 magenta. Truly arborescent in habit, it is found only 

 on the blades of the Fuci and tangles, though a few 

 float freely with the very mobile disk uppermost and the 

 long trailing tentacles hanging in the water. Indeed, it 

 loosens hold of its site more readily than most of the group 

 and its tissues are comparatively delicate^ so that when 

 tearing tangle-blades, to separate them, the rent sometimes 

 severs the anemone as well as the tangle. No sight could 

 be more beautiful than to glance along the surging sea-weeds 

 and watch the large tentacles with their hues of green and 

 red nodding with each wave. Instead of Clava muUicornis 



