POLYZOA axd tunicata. 



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animals. In the specimens which you pick up on the 

 beach nothing more than this would be seen, however 

 closely you might examine them, but in our sample just 

 taken out of the water, we shall be able to shew much 

 more. The broad orifice surrounded by spines is covered 

 during life with a very delicate elastic membrane, stretched 

 across it like the head of a drum, and towards the front 

 of this there is a slit with two lips in the form of a cres- 

 cent. From the lips of the slit a case or tube of the 

 thinnest possible skin passes through the middle of the 

 cell, within which plays a polype to and fro, capable of 

 protruding itself to a great extent, as well as of retreating 

 far into the depths of its cell, according to its pleasure. 

 In the latter state the animal is bent upon itself with a 

 double fold, somewhat like a person lying in bed with his 

 knees tucked up ; but when it wishes to expand itself, 

 two pairs of muscles, which are seen in the form of threads 

 on each side, draw the body forward, and the skin that 

 envelopes it turns inside out, just as we draw off a stock- 

 ing. It gradually protrudes from the slit as it unfolds, 

 and then displays a number of long tentacles which are 

 regularly packed side by side in a bundle ; but when these 

 are quite protruded, they suddenly expand into the shape of 

 an elegant bell or cup. The appearance of the animal is 

 now very beautiful ; it is as clear as spun glass ; the 

 sprightly motions which it exhibits increasing its beauty. 

 Each of the thread-like tentacles seems to have a double 

 row of black teeth, like the cogs of a watch-wheel which 

 run rapidly along in ceaseless course ; those of one side of 

 the tentacle running towards the tip, and those of the 

 other side towards the base. Striking and beautiful, 



