42 1'AL^EONTOLOGY. 



these are connected the nerves supplying the body segments 

 and their appendages. The body presents a corresponding 

 symmetrical form. The skeleton is external, and consists of 

 articulated segments of a more or less annular form. The 

 articulated limbs, in the species possessing them, have a like 

 condition of the hard parts, in the form of a sheath winch 

 incloses the muscles. The jaws, when present, are lateral, and 

 move from side to side. 



The worm, the lobster, the scorpion, and the beetle, 

 exemplify this province. 



The articulate division of the animal kingdom, most 

 universally distributed and numerically abundant at the 

 present day, is least perfectly represented amongst the relics 

 of the former world. Their chitinous integuments, often 

 hardened with earthy salts, are as capable of preservation as 

 the shells of the Molhisca, and remains of them are met with in 

 all aqueous deposits ; but that manifold, complex organization, 

 which in the recent state fits them so admirably for generic 

 and specific comparisons, is fatal to their entire preserva- 

 tion, and the fossil examples are often so fragmentary as to 

 admit of little more than the determination of their class 

 and family. 



The most ancient fossiliferous rocks bear imprints which 

 have been regarded as the tracks and burrows of marine 

 worms. With these are found Crustacea of the lowest 

 division, and of a group which is wholly extinct. A little 

 later appear the Phyllopods, Copepods, and other existing 

 orders of Entomostraca. Only a few obscure forms, doubtfully 

 referred to the higher division, Malacostraca, have been found 

 in the carboniferous and Permian systems. The secondary 

 strata contain abundant remains of Isopods, and of lobsters 

 and hermit-crabs. True crabs (Brachyura), rare in the newer 

 secondary rocks, abound in the oldest tertiaries. Air- breathing 

 insects and Arachnida existed even in the palaeozoic age; the 



