CRUSTACEA OF THE SEASHORE 89 



the sea-bottom is perhaps the most densely popu- 

 lated of all parts of the earth's surface. Nowhere, 

 at all events, do we find so wide a range of animal 

 forms, from the simplest organisms (Protozoa) up to 

 highly-organized Vertebrates. Nowhere, perhaps, is 

 the struggle for existence more keen, and it is not 

 without justice that some naturalists have regarded 

 the shallow waters of the sea as " one of the great 

 battle-fields of life," where, in the long course of 

 evolution, the main branches of the animal kingdom 

 have had their origin. 



Conspicuous among the animals of this region are 

 Crustacea of all sorts and sizes. To identify all the 

 species that may be obtained in a single haul of the 

 dredge in British seas would sometimes be a hard 

 task even for the most expert student of the group. 

 Our present purpose, however, is not to compile a 

 faunistic catalogue, but merely to give some idea of 

 the endless diversity of form, and to note a few of 

 the "shifts for a living" -of the ways in which 

 structure and habit are adapted to the conditions 

 of life in the Crustacea of the shore and of shallow 

 water. 



Though it might seem that the heavily armoured 

 Lobsters and the larger Crabs would be sufficiently 

 protected against most enemies when once they have 

 attained their full size, yet they are preyed upon by 

 the Octopus, which seizes them with its suckers and 

 pierces their armour with its powerful beak, injecting 



