216 CHARLES DARWIN 



they are of little general interest. I will mention only one 

 class of facts, relating to certain zoophytes in the more highly 

 organized division of that class. Several genera (Flustra, 

 Eschara, Cellaria, Crisia, and others) agree in having singu- 

 lar moveable organs (like those of Flustra avicularia, found 

 in the European seas) attached to their cells. The organ, in 

 the greater number of cases, very closely resembles the head 

 of a vulture; but the lower mandible can be opened much 

 wider than in a real bird's beak. The head itself possesses 

 considerable powers of movement, by means of a short neck. 

 In one zoophyte the head itself was fixed, but the lower jaw 

 free : in another it was replaced by a triangular hood, with a 

 beautifully-fitted trap-door, which evidently answered to the 

 lower mandible. In the greater number of species, each cell 

 was provided with one head, but in others each cell had two. 



The young cells at the end of the branches of these coral- 

 lines contain quite immature polypi, yet the vulture-heads 

 attached to them, though small, are in every respect perfect. 

 When the polypus was removed by a needle from any of the 

 cells, these organs did not appear in the least affected. When 

 one of the vulture-like heads was cut off from the cell, the 

 lower mandible retained its power of opening and closing. 

 Perhaps the most singular part of their structure is, that 

 when there were more than two rows of cells on a branch, 

 the central cells were furnished with these appendages, of 

 only one-fourth the size of the outside ones. Their move- 

 ments varied according to the species; but in some I never 

 saw the least motion; while others, with the lower mandible 

 generally wide open, oscillated backwards and forwards at 

 the rate of about five seconds each turn; others moved rap- 

 idly and by starts. When touched with a needle, the beak 

 generally seized the point so firmly, that the whole branch 

 might be shaken. 



These bodies have no relation whatever with the produc- 

 tion of the eggs or gemmules, as they are formed before the 

 young polypi appear in the cells at the end of the growing 

 branches; as they move independently of the polypi, and do 

 not appear to be in any way connected with them; and as 



not very common; although I was often searching under the stones, I saw 

 only seven individuals. No fallacy is more common with naturalists, than 

 that the numbers of an individual species depend on its powers of propagation. 



