178 IANTHINID^. 



is necessary to the existence of the animal. While on 

 this part of the subject I would call especial attention 

 to a paper by Dr. Iteynell Coates, which appeared in 

 the ' Journal of the Academy of Natural Sciences of 

 Philadelphia ' for 1826,, entitled " Remarks on the float- 

 ing apparatus, and other peculiarities of the genus Ian- 

 thina." The author's observations were made during a 

 voyage to the East Indies. As to the mode in which 

 the float is constructed, or rather repaired, he says that 

 on a living specimen being placed in a tumbler of sea- 

 water, and a portion of the appendage being removed 

 by scissors, the animal very soon commenced supplying 

 the deficiency in the following manner : — the foot was 

 advanced upon the remaining vesicles until about two- 

 thirds of it rose above the surface of the water ; it was 

 then expanded to the uttermost, and thrown back 

 upon the water, like the foot of a LimncBa when about 

 to swim; in the next place it was contracted at the 

 edges, and formed into the shape of a hood, enclosing a 

 globule of air, which was slow T ly applied to the extremity 

 of the foot. A vibratory movement could now be per- 

 ceived throughout the foot, and when it was again 

 thrown back to renew the process, the globule was 

 found enclosed in its newly constructed envelope. The 

 vesicular membrane is evidently secreted by the foot, 

 and is probably of the same nature as the byssus and 

 glutinous filaments of other mollusca. The shape of 

 the float varies according to the species. He adds, " It 

 does not appear that the janthinse ever sink below the 

 surface, when they remain attached to the vesicle ; but 

 when they are entirely separated, they immediately fall 

 to the bottom of the tumbler, and are unable afterwards 

 to rise from their position, and though they continue to 

 be vigorous for some time, they generally die in a few 



