700 COELENTERATA-II. CNIDARIA. 



an aperture through which some of its contents can be forced out. The feed- 

 ing, reproductive, and other members cluster beneath the float, and several 

 immensely long filaments, supplied with multitudes of stinging batteries, 

 trail down into the water. The stinging powers of this Cnidarian are so 

 great that adventurous people who have tried to capture a large tpecimen 

 have narrowly escaped with their lives. 



Turning now to the second great division of the Cnidaria, the Scyphozoa, 

 we find that an important change has taken place in the simple sac or tube- 

 like body. A tube has grown inward from the mouth 

 The Scyphozoa. into the body, forming a passage to the stomach (a simple 

 kind of oesophagus) ; this, being an ingrowth from 

 outside, is always lined with the outer layer of the body wall. All the 

 Scyphozoa i.e., the Jelly-fish proper, the Anemones, and the Corals are 

 distinguished by the presence of this oesophagus from the Hydrozoa above 

 described. 



In the Hydrozoa we had single stationary polyps, stationary colonies, 

 medusoid individuals which have broken loose from stationary colonies, and 

 medusse which no longer belong to any stationary form. In the Scyphozoa, 

 also, we have single stationary polyps, colonies of polyps, and free-swimming 

 medusse. Taking the last of these forms, the Scypho- 

 The medusse, first, we find not only that they are far larger 



Scyphomedusae. and more important than are the Hydromedusse, but that 

 the thickening of the middle gelatinous layer of their body 

 is even greater than in the Hydromedusse. The gelatinous tissue is a mere 

 network of connective tissue, the interstices of which are filled with water, 

 which far exceeds in volume all the delicate body tissues of the animal. This 

 is well illustrated by the fact that a Jelly-fish weighing 34 Ibs., and measur- 

 ing 7 ft. in diameter without its tentacles, when left to dry in the sun, in a 

 few d*ys lost j 9 ^ of its original weight. It has also been stated that, when 

 a large Jelly-fish is placed in the sun on blotting paper, nothing but the out- 

 line of its form has been found after a few hours have passed. 



These Scyphomedusse differ from the Hydromedusse in several ways. 



The margin of the umbrella is generally lobed, and there is no true velum ; 



the mouth at the tip of the manubrium is often square. 



An English Jelly- The cavity of the body is more complicated than in the 



Fish (Aurelta Hydromedusse, being divided up in various ways, and 



aurita). the radial canals are often richly branched. To the 



Scyphomedusse belong, not only many lovely tropical 



forms, but those commonly seen floating in our own waters. In the 



commonest of these last (Aurelia aurita) the margin forms eight slightly 



marked off lobes and is fringed with very fine tentacles. The square mouth 



is edged with four long arms, which hang down into the water and catch 



prey. At the eight notches between the lobes are small sensory bodies 



which are protected in the way characteristic of the "covered eyed" 



Medusse (as the Scyphozoa were formerly called). Four large coloured 



patches, which are very marked on the upper surface of the umbrella, 



represent the reproductive masses, beneath which the under surface of 



the umbrella is hollowed out into four pits. The water needed for 



aerating the tissues is thus brought into closer proximity to the reproductive 



elements. 



A curious modification of the ordinary form is found in the Rhizostomse 

 or Root-footed Jelly-fish. The corners of the square mouth at the tip of the 



