. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. PHOTOPERIOD AND DAILY RHYTHM 81 to account for other responses of the rhythmic mechanism of Uca; in fact, they even exhibit the same intrinsic characteristics. They are, therefore, assumed to be the same and this work is considered to provide striking support for the earlier hypothesis and to describe further properties of these two postulated centers. Figure 3 is a diagrammatic representation of the mechanism which has been hypothesized to account for the responses of the daily rhythmicity observed during these experiments.
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. PHOTOPERIOD AND DAILY RHYTHM 81 to account for other responses of the rhythmic mechanism of Uca; in fact, they even exhibit the same intrinsic characteristics. They are, therefore, assumed to be the same and this work is considered to provide striking support for the earlier hypothesis and to describe further properties of these two postulated centers. Figure 3 is a diagrammatic representation of the mechanism which has been hypothesized to account for the responses of the daily rhythmicity observed during these experiments. In conformity with the earlier work, centers A and B are here indicated as 1 and 2. With regard to the elements involved in this hypothesis, there is no reason to be concerned with the identity or non-identity of the dispersing principles whose liberation is controlled by A and B. The hypothesis requires only that there be two controlling centers, each of which has at its disposal a dispersing substancev Although it is not necessary that these two centers be physically discrete, it is possible that they are. Thus, it is of interest that both the sinus gland and the central nervous system in Uca elaborate black-dispersing substances (Sandeen,. BLAO - CONCENTRATNG " TACTOfl MELANOPHOfCS '\TACTOB OH FACTORS FIGURE 3. A diagrammatic representation of the postulated control mechanism of the black chromatophore rhythm of Uca. 1950). There is no direct evidence for the existence of a black-concentrating principle but other work done in this laboratory (Brown and Hines, in press) provides indirect support for its postulation. The complexity of this controlling mechanism leads inevitably to speculation concerning the reasons for such elaborate systems. The idea has often recurred in the invertebrate endocrine literature that chromatophorotropins are simultaneously concerned with more basic functions. If, purely speculatively, this reasoning is followed, one may ask what functions
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