New Forms of the Hemichordata. 163 



(cf. van Beneden's observations (2), in which he describes the cilia as 

 non-motile). 



Other observations were then made on animals projecting over 

 the edge of the stone so that transmitted light could be used. In 

 this case the cilia were observed to be very active, though, if the 

 animal were disturbed, they suddenly ceased before the animal 

 withdrew into the tube. On one or two occasions the cilia were 

 observed to remain at rest when the undisturbed animal was fully 

 extended. Expansion of the lophophore was not as described in 

 some species, viz., after the extension of the body, but the tentacles 

 began to spread out at the very commencement of the protrusion. 



The currents of water were best observed under the microscope. 

 It was found that what might be called the inset current, as is to be 

 expected, was into the space between the outer and inner circle. 

 Particles in suspension in the water were carried into this region 

 even from a distance equal to the length of the outstretched tentacles. 

 The particles, especially the larger, were carried to the mouth on the 

 tentacles, evidently by the active cilia. It was surprising, however, 

 to find that in many cases, after reaching the base of the tentacles 

 or margin of the mouth region, the same particles were returned on 

 the same tentacles, and travelled as rapidly in the opposite direction 

 to the distal end of the tentacle. The tip of the tentacle was then 

 slowly bent backwards, and the particle dropped off on to the stone, 

 the cilia at this part of the tentacle during the process ceasing all 

 movement. In such cases the particle was observed to have a 

 coating of mucus, by a thread of which it often hung on to the 

 tentacle for a time. In a few cases the particles were dropped off 

 in the same way without first travelling to the mouth. This was 

 observed to occur not only in the outer circle of tentacles, but also in 

 the inner, in which case they were dropped into the centre of the 

 inner circle when there was a constant and very strong current 

 passing upwards and away from the animal. The disposal of par- 

 ticles in this way seemed as much a function of the cilia as the 

 conveying of them to the mouth. I at first supposed that it was 

 effected by a reversal of the movement of the cilia, but this was never 

 observed. It was afterwards observed, however, that if a tentacle 

 be carefully examined, looking towards it from the direction of the 

 mouth region, the cilia on each side showed the ciliary movement in 

 opposite directions." This occurred on all the tentacles, both those 

 of the inner and outer row. The apparent movement may best be 

 described as upwards on the left side and downwards on the right of 



* I do not know whether such ciliary motion has been recorded in any of the 

 Polyzoa, but I have observed it in some. 



