. Senescence and rejuvenescence. Age; Reproduction. AGAMIC REPRODUCTION AND REJUVENESCENCE 151 mediately distal to the circle of proximal tentacles (m, Fig. 50). Three stages of development of the medusa bud drawn to the same scale are shown in Figs. 53-55. In the early stages the medusa bud is always more susceptible to cyanide than the adjoin- ing regions of the hydranth from which it arose, and its suscepti- biHty decreases as development proceeds, the large, fully developed bud being much less susceptible than the adjoining regions of the parent hydranth. These differences in susceptibilit


. Senescence and rejuvenescence. Age; Reproduction. AGAMIC REPRODUCTION AND REJUVENESCENCE 151 mediately distal to the circle of proximal tentacles (m, Fig. 50). Three stages of development of the medusa bud drawn to the same scale are shown in Figs. 53-55. In the early stages the medusa bud is always more susceptible to cyanide than the adjoin- ing regions of the hydranth from which it arose, and its suscepti- biHty decreases as development proceeds, the large, fully developed bud being much less susceptible than the adjoining regions of the parent hydranth. These differences in susceptibility are not dependent upon differences in size, for they concern primarily the surface of the body. Differences in motor activity may be concerned in the difference in susceptibiUty between the fully developed medusa bud and the hydranth, but the greater suscep- tibility of the bud in early stages as compared with the hydranth cannot be accounted for in this way, for motor activity is present. 'S3 54 Figs. 53-55.—Pennaria tiarella: three stages in the development of a medusa bud in the hydranth but not in the medusa bud. Evidently the medusa bud in early stages is physiologically younger than the region of the hydranth from which it arises. But the susceptibiUty of young medusa buds is in general distinctly less than that of young hydranths of the stage of Figs. 51 and 52, after emergence from the perisarc. That is, the young medusa bud is not as young as the yoimg hydranth. The medusa bud arises from a more highly specialized region of the colony than the hydranth bud and develops into a more highly specialized zooid or individual. Apparently the reconstitution of a portion of the hydranth body into a medusa bud does not carry the region concerned back to so early a physiological stage as that attained in the reconstitution of a region of the stem into a yotmg hydranth. This difference in physiological condition between hydranth bud and medusa bud is probably the dynamic basis


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Keywords: ., bookcentury1900, bookdecade1910, booksubjectreproduction, bookyea