146 THE birds' heads. 



transparency however permits the intestines to be 

 perfectly visible, and the contents of these, of a yell 

 lowish colour, are often seen whirled round and round 

 with a rapid movement, doubtless by the action of 

 internal cilia. 



But the most singular chapter in the history of this 

 polype is the presence of some curious appendages 

 which it has in common with a few more species of 

 the same family. On the outside of some (not all) of 

 the cells, in this species, there is a little tubercle near 

 the bottom, to which is articulated by a slender joint 

 an organ which has been aptly compared to the naked 

 head of a vulture. It has a beak with two mandibles, 

 of which the lower alone is moveable, opening and 

 shutting like that of a bird, but with a far greater 

 width of gape ; for the lower mandible can be opened 

 till it extends in the same line with the upper. The 

 upper mandible is furnished with five strongly pro- 

 jecting teeth on each edge; the lower has a single 

 tooth at its point, which fits into the notch between 

 the terminal pair of the upper. The whole of the 

 back of the head is wrinkled transversely. 



The motions of this strange appendage are in keep- 

 ing with its curious structure. The whole head 

 ordinarily sways to and fro upon the slender joint at 

 the poll, at intervals of a few seconds ; but besides 

 this motion, which is even, though rather quick, 

 the lower mandible, which commonly gapes to its 

 utmost extent, now and then at irregular intervals 

 closes with a strong sudden snap, much like the snap- 

 ping of a turtle's jaws, and presently again opens, and 

 leisurely resumes its former expansion. The muscles 



