VESICLES OF CORALLINES. 77 



about in a fluid. In one case described by Dr. Grant, 

 they are large, of a light brown colour, semi-opaque, 

 nearly spherical, composed of minute transparent 

 granules, ciliated on the surface, and distinctly irri- 

 table. On placing an entire vesicle, with its germs, 

 under the microscope, the cilia were seen through 

 the transparent sides, actively vibrating, and the 

 currents that were produced in the fluid within, 

 by their motion. When the vesicles were opened 

 with needles in a drop of sea water, the germs 

 were observed to glide to and fro through it, 

 at first slowly, and afterwards more quickly, the 

 cilia propelling them, with the same part always 

 forward. 



They are highly irritable, and frequently contract 

 their bodies into singular forms. This is especially 

 observable when they come into contact with a hair, 

 a filament of seaweed, a grain of sand, or any other 

 minute object. Such changes are likewise fre- 

 quently observable when a germ is busied in attach- 

 ing itself permanently to the surface of the glass. 

 After the germs are fixed, they become flat and 

 circular, and their more opaque parts radiated, so 

 that they now appear, even to the naked eye, like so 

 many minute grey-coloured stars, having the inter- 

 stices between the rays filled with a colourless 

 transparent matter, which seems to harden into 

 horn. The grey matter swells in the centre where 

 the rays meet, and rises perpendicularly, surrounded 

 by the transparent horny matter, so as to form the 



