The Effect of reversing the Internal Water-Current on the Spicule Orientation in Leucosolenia variabilis and L. complicata

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Abstract
1. Specimens grown in quiet water in an aquarium tank produce the same pattern of spicules as do those occurring naturally. Woodland's hypothesis, that the orientation arises from turbulence in the environment, is thereby disproved. 2. Reversing the internal water-current in excised oscular tubes of Leucosolenia has shown that no direct causal relationship exists between the direction of the current and the orientation of the spicules. 3. The spicule arrangement is modifiable by experiment; the orientation is not dependent on the existence of static structural features in the wall of the sponge. 4. Removal of the oscular rim has little effect on the orientation of the spicules subsequently developing in the tube behind. 5. Diverticula develop from bulges, formed largely by a reshaping process. The arrangement of the associated small spicules is essentially the same as for L. lieberkühnii. 6. A mechanical hypothesis explaining the orientation of the spicules is briefly described. The formative cell sextet is believed to be oriented by a movement of the mesogloea over the epithelium to which the sextet is contiguous.

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