CHAP, ix.] ZOOPHYTES. 201 



many observations on the lower marine animals,* but they are 

 of little general interest. I will mention only one class of tacts, 

 relating to certain zoophytes in the more highly organized divi- 

 sion of that class. Several genera (Flustra, Eschara, Cellaria, 

 Crisia, and others) agree in having singular 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 move- 

 ment, 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 evi- 

 dently 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 corallines 

 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 a 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 fur- 

 nished with these appendages, of only one-fourth the size of the 

 outside ones. Their movements 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 



* I was surprised to find, on counting the eggs of a large white Doris 

 (this sea slug was three and a half inches long), how extraordinarily 

 numerous they were. From two to five eggs (each three-thousandths of an 

 inch in diameter) were contained in a spherical little case. These were 

 arranged two deep in transverse rows forming a ribbon. The ribbon ad- 

 hered by its edge to the rock in an oval spire. One which I found, mea- 

 sured nearly twenty inches in length and half in breadth. By counting how 

 many balls were contained in a tenth of an inch in the row, and how many 

 rows in an equal length of the ribbon, on the most moderate computation 

 there were six hundred thousand eggs. Yet this Doris was certainly 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 

 rutmbers of an individual species depend on its powers of propagation. 



