. Senescence and rejuvenescence. Age; Reproduction. AGAMIC REPRODUCTION AND REJUVENESCENCE 123 that this region has undergone the first step in the process of individuation. Each one of the gradients is the dynamic expres- sion of this individuation. In fact, the body of Planaria, after a certain stage of development, is physiologically a chain of two or more zooids, , of individ- uals organically connected. In young animals four or five milli- meters long only two zooids are distinguishable, the longer, anterior zooid making up the greater part of the body and bearing the head, and the sh
. Senescence and rejuvenescence. Age; Reproduction. AGAMIC REPRODUCTION AND REJUVENESCENCE 123 that this region has undergone the first step in the process of individuation. Each one of the gradients is the dynamic expres- sion of this individuation. In fact, the body of Planaria, after a certain stage of development, is physiologically a chain of two or more zooids, , of individ- uals organically connected. In young animals four or five milli- meters long only two zooids are distinguishable, the longer, anterior zooid making up the greater part of the body and bearing the head, and the shorter, posterior zooid indi- cated only d3TiamicaUy by a second metabolic gradient in the posterior region. The boundary between the two zooids in these small animals is indicated by the dotted line across the body in Fig. 28. As the animal be- comes longer, other zooids arise in the posterior region by fur- ther physiological division of the original posterior zooid, and when it has reached a length of Figs. 28-30.—Development of zooids in Planaria dorolocephala: Fig. 28, a young animal with two zooids, i and 2; Fig. 29, a half-grown animal in which the original posterior zooid has divided into zooids and , and has vmdergone further division; Fig. 30, a full-grown animal in which still further zooids have 2. 28 u + 30. 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 Child, Charles Manning, 1869-1954. Chicago, Ill. , The University of Chicago Press
Size: 1795px × 1392px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, booksubjectreproduction, bookyea
