37 



CLASS II. ACALEPHA. 



(SEA-BLUBBERS.) 



THE most common form of these animals is that 

 of an umbrella, or a mushroom ; a broad circular 

 convex disk of jelly, usually clear and colourless, 

 but sometimes having the frosted appearance of 

 ground glass, and sometimes being tinged with 

 delicate colours. From the under-surface or in- 

 terior, called the sub-umbrella, commonly depends 

 a fleshy mass called the peduncle, representing the 

 handle of the umbrella, or the stem of the mush- 

 room : sometimes this is slender and of consider- 

 able length, but more commonly it is thick, and so 

 short as not to protrude below the level of the 

 margin ; it usually terminates in four expanding 

 triangular lips, which are often much frilled and 

 fringed at their edges. The centre of these four 

 lips is the mouth, which leads to a cavity (the 

 stomach) in the upper part of the peduncle, where 

 the food is digested. Slender vessels radiate from 

 this cavity, across the convexity of the "umbrella," 

 to the circumference ; where they open into another 

 vessel, which runs completely round the margin. 

 In all these vessels the nutritive fluid circulates 

 from the stomach, as may be readily seen with a 

 microscope, by the motion of the particles. 



From the circumference generally proceed thread- 

 like tentacles, varying in number and length, 

 which are very sensitive, have great power of con- 

 traction, and are studded with capsules inclosing 

 poison-threads, exactly resembling those of the 

 tolypes, and serving the very same purpose, viz. 



