HALF AN HOUR WITH JELLY-FISH. 107 



jelly-fish (Aurelia aurita). Not only is it a familiar 

 object, but its beauty is equal to any of its congeners. 

 It averages from six to eight inches in diameter, but 

 is often larger, especially off the southern coasts. 

 Its common name is given to it on account of the 

 four crimson-coloured rings which may be seen 

 relieving the otherwise glassy body. This species 

 swims by the regular contraction and expansion of 

 the body, and is theref ore placed among the pulmoni- 

 ffrade jelly-fish, on account of the pulsations which 

 propel it through the water resembling those of the 

 lungs. The crimson rings mentioned are reproduc- 

 tive organs. Generally speaking, most of the bell- 

 shaped or umbrella-shaped jelly-fish have peculiar 

 organs hanging down their interior, much as a bell 

 clapper hangs from the inside of a bell. These are 

 called the polypite, and their functions are digestive, 

 or alimentary. In the case of the species we are 

 mentioning, a kind of pouch may be seen terminating 

 the margins of the polypite, and it is now known 

 that this is for ova. When the young are extruded 

 they swim away as minute, flat, jelly-like bodies, 

 aided by cilia, the usual method of progression with 

 the ova of animalcule and other creatures, and even, 

 as we saw in the " seaweeds," with the spores of 

 those plants. 



Let us follow these little ova after their extrusion. 

 The first thing noticeable is their shape, which is so 

 flat, that when in this stage they were regarded as 

 a distinct species, and went by the name of Planula. 



