RHAfibOPLEURA MltlABtLlS. 33 



Polyzoa. Its enormous development in the present instance 

 seems, however, to indicate that it must have a very peculiar 

 and important function in the economy of this animal. My 

 observations on the living animal have also guided me to a 

 decided opinion, to which, however strange it may appear, I 

 have been forced again and again to return, and which I 

 therefore must retain, namely, that the animal uses this 

 buccal shield (according to my observations) as a sort of 

 creeping organ, by means of which it can draw itself up to the 

 aperture of its tube. Since, as above stated, both endocyst 

 and all muscles of proti'usion are wanting, it is in reality 

 quite inexplicable how the polypide, which is often found 

 drawn back, not only to the bottom of the free cell, but even 

 partially into the corresponding chamber of the creeping 

 stem (see fig. 6), should be able in any other manner to get 

 forward again so far as to the aperture of the cell. It 

 might, perhaps, be supposed that this could be eflPected by 

 means of the elasticity of the contractile cord ; but I have 

 convinced myself that such is not the case, by cutting 

 through the contractile cord at its base ; the polypide has 

 continued undisturbed its slow protrusion, and has also at 

 length really reached the opening of the cell without any 

 remarkable change. The direct observations made on the 

 uninjured animal have also confirmed me in the view ex- 

 pressed above. It will be seen that during the slow pro- 

 trusion of the polypide (which often lasts for hours) 

 the buccal shield is always in immediate contact with the 

 wall of the tube, the whole of its ventral side being closely 

 pressed up against the same; it retains this position un- 

 changed as long as the protrusion lasts ; and the protrusion 

 does not stop until the whole length of the buccal shield is 

 extended outside of the aperture of the cell ; then the Poly- 

 pide is completely expanded. On examining more closely 

 this buccal shield we observe in the middle of it an 

 opaque part, which seems to contain an interior glandular 

 organ. Continuing the investigation, and slightly pressing 

 the animal, we notice, however (fig. 2), that this opaque 

 appearance is not produced by any such internal organ, but 

 by a peculiar and seemingly muscular structure of the 

 substance of the shield itself. It exhibits, seen from below, 

 in the middle numerous small bubbles, situated rather far 

 from each other, or somewhat irregularly formed small cells, 

 which, however, when more closely examined (and this is 

 particularly evident in those which lie nearer to the periphery 

 of the disc), show themselves to be the external rounded ex- 

 tremities of small, inwardly prolonged cylinders, which 



VOL. XIV. NEW SER. C 



