THEIR PROBABLE USE. 147 



which move the lower mandible are distinctly seen, 

 occupying the position of the palate, and extending 

 back to the inner surface of the skull, if we may use 

 such terms for an organization so remote. These 

 motions are highly singular to witness, and one can 

 scarcely look upon them without ascribing them to 

 an active volition in the animal. 



But curious questions arise in connection with 

 these birds' heads. Are they a part of the organiza- 

 tion of the polype ? If so, why are they found 

 attached to some cells, and not to others? why to 

 some specimens and not to others ? and why are some 

 species of a genus furnished with them, while others, 

 essentially the same in every other respect, are desti- 

 tute of any such appendage ? 



Anatomical examination does not throw any light 

 on these questions. The animal within the cell appears 

 to be organically independent of the bird's head, for 

 as Dr. Reid affirms, and as I have myself witnessed 

 in another species, the latter continues its movements 

 for a considerable time after the polype has been dead. 

 Dr. Johnston suggests that the use of the organ is to 

 grasp and kill passing animalcules, which then may 

 be drawn into the cell by means of the ciliary currents 

 of the tentacles ; and this seems to me not improba- 

 ble, and receives confirmation from the toothed 

 structure of the beak, which, though strongly marked, 

 I have not seen noticed. Plate YII. Fig. 1. Cella- 

 laria ciliata, nat. size. 2. a portion of a branch, 

 (magnified 200 diameters.) 3. a cell containing the 

 contracted polype. 4. the bird's head appended to 

 it. 5. an immature cell. G. the bird's head more 



