SEA-ANEMONES AND THEIR ALLIES. 77 



rise to a number of large jelly-fish. There seems almost 

 no limit to the size a jelly-fish may reach, but specimens 

 of Aurelia aurita round our coasts commonly vary from 

 six inches to a foot or more in diameter. If this be com- 

 pared with the minute size of the hydra-tuba, and the 

 relative sizes of the sea-firs and their swimming-bells be 

 recalled, it will be clear what is meant by the statement on 

 page 64 that in the alternations of generations seen in the 

 jelly-fish, the free-swimming stage is accentuated at the 

 expense of the sedentary stage. 



To get a general idea of the structure of a jelly-fish, some 

 specimens of Aurelia aurita should be obtained. They are 

 usually very abundant in August, and care should be taken 

 to obtain one or two living specimens not too large to be 

 readily observed. The living animal is much more attractive 

 than the flattened, half-melted creature so often left on the 

 beach by the ebbing tide. In it the umbrella is sharply 

 curved, not flat as in dead or relaxed specimens, and its 

 slightly inturned margin is furnished with numerous slender 

 tentacles of perhaps a couple of inches in length; after 

 death these are always much contracted and become incon- 

 spicuous. The manubrium, or clapper of the bell, is divided 

 into four somewhat short arms, having the mouth opening 

 in the centre. You should not fail to notice that in some 

 others of our jelly-fish (Oyanea, Chrysaora) the tentacles 

 are very long, and so are also the frilled and puckered arms 

 of the manubrium. As to the other characters of Aurelia^ 

 the four horseshoe -shaped reproductive organs are very 

 obvious, and by turning the animal over you see that 

 beneath each of these is a little pit, opening to the exterior 

 by quite a distinct orifice. These are often called "respira- 

 tory" or genital pits, but are believed by some authorities 

 to be remnants of larval structures. There is no "veil" 

 like that of the swimming-bells, but the jelly is traversed 

 as in them by a series of radial canals, in this case rendered 

 very obvious by their violet tint. At the margin of the 

 bell there are eight sense-organs, or " tentaculocysts," which 

 are easily made out. 



Related to Aurelia there are, as already mentioned, some 

 other jelly-fish, often of large size, and sometimes with very 

 distinct stinging power. The very large forms are more 



