PALEONTOLOGY 



311 



More often only a part of an animal is represented by its fossil, 

 and usually only the hard parts are left. In the vertebrates the bones 

 of the skeleton are commonly preserved; in insects and Crustacea, the 



Fig. 211— Mammoth found frozen in Siberia in 1901. Most of the flesh was still on 

 the bod J' and intact. The skin is mounted in the museum of Petrograd in the posture in 

 — -' ^ " ' '" - ,,. - . „ . . Courtesy of Macmillan Co.) 



which it was found. (Fro7n Lull's Organic Evolution. 



chitinous external skeleton; in mollusks, the shell; in corals, the calcare- 

 ous tubes (Fig. 212). Fleshy parts usually decompose too soon to leave 



-f'.^- 21-.— Fossil of chain coral, Ilalysites, found in Michigan, demonstrating that 

 Michigan was once covered with marine waters and illustrating the principle that it is the 

 hard parts of animals that are preserved. (Fro?n specimen in the Museum of Geology, 

 Umversity of Michigan.) 



an impression of their form in the hardening rock layers. Nevertheless, 

 occasional fossils of soft animals are found; and in rare instances minute 



