BELOW THE TIDEMARK 267 



the rocks defy any reasonable explanation on grounds either 

 of sexual or natural selection, and emphasise the primal 

 tendency of nature to produce varied forms of beauty with 

 which the laws of selection then proceed to work. Unmated 

 organisms without eyes cannot be supposed to appreciate 

 each other's beauty, whatever may be the case with sea-fowl 

 or pheasants, and it has yet to be shown that the colours of 

 sea-anemones serve a warning purpose such as is attributed 

 to the bold markings of wasps and certain caterpillars. 



The beauty of sea-shells is apparent to all ; and it tends 

 to make us forget that every shell has been a home, or 

 rather an intrinsic part, of a creature at least as wonderful. 

 The living owner of a shell is apt to be regarded as a 

 nuisance rather than an object of interest, and there is some 

 excuse for this annoyance in its sulky and defensive attitude 

 when disturbed. To watch the ways of living molluscs satis- 

 factorily it is necessary to keep them in aquaria, or to study 

 them on the shore with experience and knowledge ; but even 

 a slight comprehension of their living habits adds enormously 

 to the interest of their dead frames. Cockle-shells are 

 among the soberest on the beach, with their plain white 

 ribbing ; nor, when we find a pair of the empty shells 

 cohering in the simulation of life, is it easy to regard the 

 cockle as an agile creature. Yet it can move through the 

 wet sand in which it lives with very tolerable rapidity, by 

 thrusting out its fleshy foot and pushing itself backwards in 

 a series of jerks. The long narrow razor-shells which we 

 find strewn on sandy shores have the same habits and system 

 of propulsion. These two shell-fish, like the oyster and the 

 mussel, are diverse forms of the bivalve group of molluscs, 

 which are not found on dry land, though the large fresh- 

 water mussel is common in fresh-water lakes. But the dead 

 shells about high-water mark and the live ones in the pools 



