BRITISH TUNICATA. 



and opens itself frequently. All the radii are of this 

 structure ; hut their common center, which is formed 

 by a combination of all the small converging ex- 

 tremities, exhibits an opening of a circular, oval, or 



FIG. 120. Botryllus Schlosseri incrusting Fucus serratus. Natural 

 size. (After Gaertner, loc. dt., pi. iv, f. 1.) a, variety with lanceo- 

 late rays ; b, with ovate-lanceolate rays ; c, with linear rays. 



oblong figure, forming a kind of rising rim like a cup, 

 which, when the animal is alive and at rest, contracts 

 and expands itself to many different degrees, with 

 great alertness and velocity, though sometimes it 



