ZOOPHYTES. 



275 



scattered by the wind from some neighbouring 

 tree, is the Broad-leaved Hornwrack (Flustra 

 foliacea). If held up to the light we can see 

 plainly that it is composed of clusters of cells. 



These cells are formed on both sides of its sub- 

 stance, and their raised margins make the surface 

 so rough to our touch. When placed under the 

 microscope, we can see that the upper part of the 

 margin of each cell is armed with four projecting 

 horny spines, which appear to be designed as a 

 protection to the polypes when they extend their 

 arms. It has been observed, too, by Dr. Farre, 

 that the transparent horny cell which closely sur- 

 rounds the body of the animal, is nearly unyield- 

 ing at the lower part, but is terminated at the 

 T2 



