IK) THE INHABITANTS OF THE SEA. 



The composition of the waters has also a most important 

 effect on the distribution of aquatic animals, as the degre/ of 

 saltness or freshness determines the presence or absen/e of 

 numerous forms of both fishes and invertebrate animals/ and 

 last, not least, the influence of depth, in which pressure and 

 the diminution of light are doubtless important elem/nts, is 

 everywhere manifest over the ocean, " for everywhere we find 

 creatures, whether animal or vegetable, distributed in successive 

 belts or regions, from high-water mark down to thff deepest 

 abysses from which living beings have been drawn up. / Peculiar 

 types inhabit each of the zones, and are confined wfthin their 

 destined limits, whilst others are common to two o/more, and 

 not a few appear capable of braving all bathymetricaJ conditions. 

 Nevertheless, so marked is the appearance of the inhabitants of 

 any given region of depth, that the sight of a su$cient assem- 

 blage of them from any one locality will enable the naturalist 

 at once to declare the soundings within certan limits, and 

 without the aid of line or plummet." / 



In the British seas four distinct and well-n/arked zones of ■ 

 life succeed each other in vertical extension. Tie first of these 

 is the littoral zone, equivalent to the tract betreen tide-marks, 

 but quite as manifest in those portions of the' coast-line where 

 the tides have a fall of only a foot or two, A even less, as in 

 districts where the fall is very great. Thi important belt, 

 which again forms four subdivisions, and' is inhabited by 

 animals and plants capable of enduring periodical exposure to 

 the air, to the glare of light, the heat of t|e sun, the pelting 

 of rain, and often to being more or less flooded with fresh 

 water when the tide has receded, claims i|any genera as well 

 as species peculiar to itself. " The verge of Jontinual air is gene- 

 rally distinguished by the abundant presence of Fucus canali- 

 culars, among whose roots may be foihd crowds of small 

 varieties of the periwinkle, called Littorinl rudis, which indeed 

 range out of the water considerably, and i/ay be found adhering 

 to rocks many feet above high-water majt." The second sub- 

 region is marked by the abundance of I small dark rigid sea- 

 weed, called Lichi/na, painting the rock ides as if with a dingy 

 stripe. With it we find the larger for/is of Littorima rudis, 

 abundance of the common limpet (Paella vulgata), the com- 



