. The Danish Ingolf-Expedition. Scientific expeditions; Arctic Ocean. Text-fig. A. Diagram showing the arched development of the pores in Pliobothrus symmetri- cus during the growth of the colony. is reduced on the hind surface of the colony; what may be the cause of this our imperfect knowledge of the biological conditions of the Stylasteridae does not enable us to explain. If we grind down the branches to about the median longitudinal plane we are able to see the pores in the whole of their length (PI. Ill, figs. 19 and 20) and it becomes apparent that these have a typical bend in their cour
. The Danish Ingolf-Expedition. Scientific expeditions; Arctic Ocean. Text-fig. A. Diagram showing the arched development of the pores in Pliobothrus symmetri- cus during the growth of the colony. is reduced on the hind surface of the colony; what may be the cause of this our imperfect knowledge of the biological conditions of the Stylasteridae does not enable us to explain. If we grind down the branches to about the median longitudinal plane we are able to see the pores in the whole of their length (PI. Ill, figs. 19 and 20) and it becomes apparent that these have a typical bend in their course, curving inwards towards the longitudinal axis of the branch and then downwards towards its base. The pores — especially the gasteropores — are of varying length; the terminal pores are, as a rule, quite short and much shorter than those we find further in on the branches. This indicates a terminal and centrifugal growth in the branch and gives us the key to the understanding of the bent course of the pores (Text-fig. A). The pores are first formed at or near the tip of the branch and approximately in its longitudinal direction; during the growth of the branch the pore is gradually moved down on its cylindrical part. The plane of the opening of the pore lies at each place approximately at right angles to its longitudinal axis and the latter will therefore become curved during the growth of the branch, as will be seen from the ac- companying diagram. A few of the gasteropores open into large, irregular, longitudinal canals, which are formed secondarily in the central part of the branch; often however their base is formed of one or two tabulae. In their original form the gasteropores are cylindrical with a slightly expanded basal part in which the zooid is attached; but during growth the gasteropores often assume a more irregular appearance. The dactvlopores also are of varying depth; they are cylindrical, more or less curved and have a slightly constricted opening region;
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectscientificexpedition
