STEUCTUrvE OF THE MEDUSA. 11 



extends to a tolerably close imitation by different 

 species of the various forms which are characteristic 

 of di^^erent species of mushrooms, from the thimble- 

 like kinds to the saucer-like kinds. Moreover, 

 this accidental resemblance to a nmshroom is in- 

 creased by the presence of a central organ, occupy- 

 ing the position of, and more or less resembling 

 in form, the stalk of a mushroom. This or£ran is 

 called the " manubrium," on account of its looking 

 like the "handle" of an umbrella, and the term 

 " umbrella " is applied to the other portion of the 

 animal. The manubrium, like the umbrella, varies 

 much in size and shape in different species, as a 

 glance at any figures of these animals will show. 

 Both the manubrium and umbrella are almost 

 entirely composed of a thick, transparent, and non- 

 contractile jelly ; but the whole surface of the 

 manubrium and the whole concave surface of the 

 umbrella are overlayed by a thin layer or sheet 

 of contractile tissue. This tissue constitutes the 

 earliest appearance in the animal kingdom of true 

 muscular fibres, and its thickness, Avhich is pretty 

 uniform, is nowhere greater than tliat of very thin 

 paper. 



The manubrium is the mouth and stomach of the 

 animal, and at the point where it is attached to or 

 suspended from the umbrella its central cavity 

 opens into a tube-system, which radiates through 

 the lower or concave aspect of the umbrella. This 

 tube-system, which serves to convey digested ma- 

 terial and may therefore be regarded as intestinal 

 in function, presents two different forms in the two 



