318 LIFE BY THE SEASHORE. 



depths. Indeed, it is well known that certain Echinoderms, 

 for instance, have a very wide range in depth. Generally, 

 we may say that in most cases depth of water does not in 

 itself determine distribution, taking depth in this case as 

 including only those comparatively trifling variations which 

 occur in the vicinity of the shore, and are to be measured in 

 unit fathoms. It may thus be asked, Is there really such a 

 thing as littoral fauna at all, or do the familiar forms of 

 the coast go down into the great depths 1 Before we answer 

 this question, suppose we in imagination begin a series of 

 dredgings off a rich coast, beginning operations quite near 

 the shore in water of eight to ten fathoms, and sailing straight 

 outwards. In our first hauls it is probable that we would 

 get no form which was not already more or less familiar on 

 the rocks. We would miss such shallow-water animals as 

 the periwinkles and the shore crab, but we should probably 

 get plenty of sea-urchins and starfish, various spider-crabs, 

 hermit-crabs, Galathea and swimming-crabs, sea-firs, and so 

 on, all animals which we know already on the rocks, though 

 the species might be different. As we progressed outwards 

 not a few familiar forms would disappear, and others would 

 appear, but it is nevertheless true that we might take a 

 series of dredgings from the East Coast of Scotland across 

 the North Sea to the coast of Denmark, without ever 

 losing sight of some characteristic littoral forms, especially 

 certain Echinoderms. Further, in the course of our journey 

 we should nowhere find a depth exceeding fifty fathoms. 

 From these observations then we should conclude that the 

 littoral fauna must at least extend down to fifty fathoms, 

 though, except some of the Echinoderms, there are not very 

 many species which can live equally well in water of a few 

 fathoms depth and that of fifty or more. 



If, on the other hand, we took our series of dredgings 

 on the West Coast of Scotland, we should find somewhat 

 different conditions. In the first place we should get into 

 deep water more quickly, and in our journey westward 

 would soon cross the fifty-fathom line. If we went onwards 

 we should find the percentage of familiar species and 

 familiar genera decreasing as we approached the hundred- 

 fathom line. After this the sea-bottom slopes somewhat 

 rapidly down to the great depths, to be measured in 



