. Elements of biology, with special reference to their rôle in the lives of animals. Biology; Zoology. T U B y B tion in regulating development of form (p. 282) then applies to the processes of regeneration as well as in the development of the adult from the embryo. Curiously enough, frag- ments of some planaria, and of other forms as well, may be made to develop two heads, one at each end of the re- generating fragment (Fig. 195). In such cases the polarization, that is, the relation of dominance and subordina- tion which ordinarily determines that one region shall become the head be- cause o
. Elements of biology, with special reference to their rôle in the lives of animals. Biology; Zoology. T U B y B tion in regulating development of form (p. 282) then applies to the processes of regeneration as well as in the development of the adult from the embryo. Curiously enough, frag- ments of some planaria, and of other forms as well, may be made to develop two heads, one at each end of the re- generating fragment (Fig. 195). In such cases the polarization, that is, the relation of dominance and subordina- tion which ordinarily determines that one region shall become the head be- cause of its higher metabolic activity, has been obliterated, and both cut surfaces, being equally independent and equally active, regenerate heads. It has been set forth that the ana- tomical characteristics of an animal are determined by the degree of com- plexity of its various organ systems (Chapters V and VI). Similarly, many of the physiological characteristics of an animal are by its rela- tive properties of growth, differentia- tion, regeneration, and agamic repro- duction. When differentiation in the adult is sharp, the other three proper- ties are reduced or lacking; differentia- tion in an adult human is high and the animal no longer grows nor re- generates nor reproduces agamically. Thus Man and other mammals in general are regarded as the most highly differentiated forms of. Fig. 195.—Regeneration of pieces from different regions of a planarian worm. C is a biaxial form; the piece was cut in such fashion that neither end dominated the other during the regeneration of the head; hence two heads were 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 Buchanan, James William, 1888-. New York, London, Harper & brothers
Size: 996px × 2508px
Photo credit: © Paul Fearn / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookpubl, booksubjectbiology, booksubjectzoology
