296 G. p. BIDDER 



10 or even 20 inches before coming to rest.^ Speaking exactly, 

 it does not really come to rest at this distance, but reaches a 

 velocity not higher than that of the slow return-current, shghtly 

 indicated in Text-figs. 2 and 3, which is necessarily established 

 to fill up the region from which this water has been removed. 



Text-fig. 4 is a diagram of the currents which must exist 

 around a bath-sponge in still, deep water. The swift vertical 

 jets from the oscula on the top surface carry the used and 



Text-fig. 3. 



4»r *> » *- •k»-»-S»»»>. 



10 Cnx 



fouled water to a stratum some feet above the sponge ; slow 

 currents, in the plane at right angles to the jets, creep in from 

 all directions along the sea-bottom to feed the intaking porec, 

 which cover the general surface of the sponge. If the water 

 be absolutely still, there is estabhshed between these afferent 

 and efferent currents a re-entrant vortex, whose section is 

 a, circle in any radial plane through the osculum. 



The diameter of that circle I call the Diameter of Supply ; 

 and the angle between the directions of the intake and outflow 

 currents, which in sessile sponges (Text-fig. 4) is a right-angle, 

 and in pedunculated sponges (Text-figs. 9 and 10) is 110° to 

 120° or more, I call the Angle of Supply. 

 1 See Note 5, (12). 



