238 Dr. J. D. F. Gilchrist on 



zooids and buds. These cilia, except on the arms, are rather 

 fine, and in some places could be seen with difficulty with a 

 Zeiss lens; but the energetic movement of the surrounding 

 water which they brought about was very apparent in the 

 small particles of various kinds of matter which they caused 

 to move rapidly over the surface. The direction of such 

 movement, both in zooid and bud, was from the attached 

 towards the free end. Thus, in the case of the zooid, particles 

 were seen to move rapidly up the stalk and over the visceral 

 region of the body towards the arms. The details of their 

 further progress could best be seen in a detached arm. In 

 this an active stream of particles was seen passing rapidly 

 over the tentacles on each side of the arm towards its distal 

 extremity ; most of these were discharged into the water, 

 but now and again a particle was observed to pass along the 

 central groove of the arm in the opposite direction towards 

 the mouth. This groove, which is broad and shallow, was 

 seen to be provided with stronger and longer cilia than 

 occurred elsewhere. Cilia on the tentacles were much 

 smaller even than those on the body, and could with diffi- 

 culty be made out, and, but for the active movement of 

 particles near them, their existence might have been doubted. 

 The active jeiking movement already noted was apparently 

 mainly in the tentacles, and seems to be associated with the 

 feeding process — perhaps the selection of particles fit for food 

 to be returned to the mouth by the groove in the arms. It is 

 of interest to compare this method of feeding with what I 

 have described elsewhere (i) for Phoronis. Here the body 

 is enclosed in a tube, which the animal never leaves, and 

 it is not ciliated. Food and other particles are brought in 

 a current of water, which passes inwards between the outer 

 and inner circle of tentacles, and flows outwards between the 

 tentacles. Some of these particles are in some way selected, 

 and are passed down into the food-groove running round the 

 inner base of the tentacles towards the mouth. This food- 

 groove may be enlarged by a low web of tissue connecting 

 the tentacles slightly at their bases, and it is at once suggested 

 that the arms of Gephalodiscus are outgrowths or extensions 

 of such a food-groove, while the tentacle on each side of the 

 arms may be compared to those of Phoronis, which exhibit 

 the characteristic jerking movement — a sudden flexing 

 inward from the tip, — perhaps in connection with the selection 

 of the food-particles out of the many passing over them. 

 The absence of arms and tentacles in the collar-region of 

 Balanoglossus is associated with the more indiscriminative 

 manner in which it procures its food. The manner in which 



