. Animal biology. Zoology; Biology. 520 GENERAL CONSIDERATIONS arches (Fig. 245), the gradual development of the vertebral column to replace the primitive notochord, and the development of the different types of excretory system (Fig. 216), all of which have been previously noted. Paleozoology offers very many evidences that life has gradually changed. Apparently no rock strata exist which show traces of the. A B C D E F G Fig. 318.—Parallel stages in the development of several vertebrates. A, fish; B, salamander; C, turtle; D, chick; E, pig; F, calf; G, rabbit; H, man. In each series,
. Animal biology. Zoology; Biology. 520 GENERAL CONSIDERATIONS arches (Fig. 245), the gradual development of the vertebral column to replace the primitive notochord, and the development of the different types of excretory system (Fig. 216), all of which have been previously noted. Paleozoology offers very many evidences that life has gradually changed. Apparently no rock strata exist which show traces of the. A B C D E F G Fig. 318.—Parallel stages in the development of several vertebrates. A, fish; B, salamander; C, turtle; D, chick; E, pig; F, calf; G, rabbit; H, man. In each series, a is an early stage, showing the pharyngeal slits; b, a later stage, in which the first two have developed gills and the last six show the pharyngeal slits disappearing and limits and tails developing; c, a still later stage, in which the differences between the reptile and bird on the one hand and the mammals on the other have become pronounced, marked resemblances between those of each group persisting. {From Guycr, ''Animal Biology," after Haeckel, through Romunes.) earliest life. This is due to metamorphism (Sec. 583). The older rocks give only indirect evidence of the existence of life on this earth. The earhest of the sedimentary rocks to contain an abundance of fossil types belong to the Cambrian period. Since that time strata deposited, one after another in order of time, show the appearance of many types which have gradually increased in numbers and variety, have reached a climax, then have declined, and finally have become extinct. Others have been able to maintain themselves to the present. But there has been a steady. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Wolcott, Robert Henry, 1868-1934. New York ; London : McGraw-Hill Book Company, Inc.
Size: 1764px × 1417px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookcoll, booksubjectbiology, booksubjectzoology
