MOLLU8CA. 305 



When the floating body is large, and well capable of 

 supporting the clustered barnacles, the latter have no 

 aeriferous float ; but this organ appears to be formed 

 gradually, and as a precautionary measure, when the 

 object to which the animals are attached is small and 

 fragile, or when no extraneous body can be obtained. 

 When detached from their float, they sink in sea- 

 water. 



Some examples we captured possessed clusters of small 

 round eggs, deposited between the animal and the back 

 of its shell. Some of the eggs had the blue-green co- 

 lour of the parents' shell, whilst others were orange- 

 colour. In other shells we found, together with the 

 barnacle-fish, more than six small worms, of dark co- 

 lour, annulose, and furnished with tufts of hair on their 

 sides, like aphrodites. They had numerous feet, ar- 

 ranged in two lateral rows on the abdomen, and with 

 these they moved actively, like caterpillars. 



THE PYROSOME. 

 (Pyrosoma Atlanticum.} 



The Pyrosome is, strictly speaking, an aggregate 

 tunicary, or body composed of an aggregation jf small 

 animals, perforated at both extremities, united at their 

 bases, and inclosed in a common membrane or tunic. 

 I shall, however, for the convenience of description, 

 speak of it as of one complete animal. 



The average size of the specimens we procured, 

 was from four to six inches in length, and from one-and- 



VOL. II. X 



