204 LOWER MARINE ANIMALS. [chap. ix. 



In Tierra del Fuego, as well as at the Falkland Islands, 

 I made many observations on the lower marine animals,* 

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

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

 highly-organised division of that class. Several genera 

 {Flttstra, Eschara, Cellaria^ Crisia, and others) agree in 

 having singular movable organs (like those of Flustra 

 aviculariay 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 

 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 ofl 

 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 furnished 

 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 forwards at the rate of about 

 five seconds each turn ; others moved rapidly and by 



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

 sea-slug was three and a half inches long), now 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 adhered by its 

 edge to the rock in an oval spire. One which I found, measured 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 numbers of an 

 i'nrf'T'iefu^l species depend on its powers of propagation. 



