Probably the most important of all Crustacea, however, as regards their destructive activity, are the species which bore into wood, and sometimes do extensive damage to the submerged timber of piers, jetties, and similar structures. On our own coast the most destructive is a little Isopod known as the "Gribble" (_Limnoria lignorum_--Fig. 80), which is distributed from Norway to the Black Sea, and occurs also on the Atlantic coast of North America. Several species of the same genus having similar habits are found in other parts of the world. The Gribble was first discovered as a British species by Robert Stevenson, the celebrated lighthouse engineer, who found it in 1811 destroying the woodwork employed in the erection of the Bell Rock Lighthouse, and sent specimens to Dr. Leach of the British Museum. The animal is only about one-eighth of an inch in length, and its cylindrical burrow is about one-fifteenth of an inch in diameter, and penetrates for a depth of one or two inches. The excavation of the wood is effected by means of the mandibles, which are unusually strong; and when the animals are numerous the burrows are driven so close together that the surface of the wood is reduced to a spongy mass which is rapidly washed away by the waves (Plate XXXII.). The Gribble is often accompanied by another Crustacean of similar habits, the Amphipod _Chelura terebrans_. The latter is about one-fifth of an inch in length, and differs from most Amphipods in having the body somewhat flattened from above downwards instead of from side to side. The burrows made by _Chelura_ are shallower than those of the Gribble, and generally run more or less parallel to the surface of the wood. [Illustration: _PLATE XXXII_ PIECE OF TIMBER FROM RYDE PIER SHOWING DAMAGE CAUSED BY _Limnoria_ AND _Chelura_ (_From Brit. Mus. Guide_)] CHAPTER XII CRUSTACEA OF THE PAST Since the acceptance by naturalists of the theory of Evolution as indicating the mode of origin of the various forms of life now existing, one of the chief lines of biological investigation has had for its object the reconstruction of the pedigree (or, as it is called, the "phylogeny") of the larger groups of the animal and vegetable kingdoms. In attempting to do this, there are three main sources from which evidence may be drawn. The results of Comparative Anatomy enable us to decide with more or less confidence as to the degrees of relationship between the groups of organisms, and to distinguish between the more primitive and the more specialized; the study of Embryology is, at least, an indispensable adjunct to Comparative Anatomy, even if it does not, as was once supposed, give us an actual recapitulation of ancestral history; and, finally, the study of Fossil Remains holds out the hope that we may be able to find the ancestral types themselves.