The elementary nervous system elementarynervou00park Year: [c1919] THE ELEMENTARY NERVOUS SYSTEM ligature they at once recommenced. From these obser- vations it is quite clear that the osculum controls in a purely mechanical way the current within the sponge. When the osculum is open, this current may run; when it is closed, the current ceases even though the dermal pores are open and the choanocytes continue to beat. In view of these facts the oscular ends of the fingers of Stylotella were regularly removed. Although the presence of a pore current is conclusive evidence of the open conditio
The elementary nervous system elementarynervou00park Year: [c1919] THE ELEMENTARY NERVOUS SYSTEM ligature they at once recommenced. From these obser- vations it is quite clear that the osculum controls in a purely mechanical way the current within the sponge. When the osculum is open, this current may run; when it is closed, the current ceases even though the dermal pores are open and the choanocytes continue to beat. In view of these facts the oscular ends of the fingers of Stylotella were regularly removed. Although the presence of a pore current is conclusive evidence of the open condition of the pores, its absence FIG. 6.—Diagram of a finger of Stylotella from which the tip has been cut showing cur- rents entering the subdermal spaces and emerging from the cloaca. is not proof that the pores are closed even supposing that the oscular end is cut off, for it is conceivable that the choanocytes may cease to beat, in which case the cessa- tion of the currents would be misleading as to the condi- tion of the pores. To meet this difficulty a simple pro- cedure was adopted. If the oscular end of a finger of Stylotella is cut off at some distance from the osculum itself, the cut face includes not only the cloaca and some of the flagellated chambers, but also the subdermal spaces (Fig. 6). An examination of the currents from such a cut end will show a large, slow, central current emerging from the cloaca, and a considerable number of smaller more rapid currents entering the surrounding subdermal
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