CHAPTEE IX 



TEE CCELENTERATES JELLY-FISHES, ANEMONES, 

 AND THEIR ALLIES 



ONE of the most interesting groups of marine life is that including 

 jelly-fishes and anemones. In it are the pretty little sea firs, so 

 often mistaken for sea-weeds by the youthful admirers of these 

 plants, who almost always include them in their collection of marine 

 algce ; the transparent, bell-shaped jelly-fishes, which may often 

 be seen in thousands during the summer, carried by the tides, and 

 swimming gently by graceful contractions of their bells ; and, most 

 beautiful of all, the lovely anemones the ' sea flowers' of the 

 older naturalists, by whom they were regarded as forms of vege- 

 table life. 



The simplest animals of this group are minute jelly-like crea- 

 tures, of a more or less cylindrical form, 

 usually fixed at one end, and having a 

 mouth at the other. The body is a simple 

 hollow cylinder, the wall of which is 

 made up of two distinct layers, while 

 the cavity within serves the purpose of 

 a stomach. The mouth is surrounded by 

 a circle of arms or tentacles by means of 

 which the creature is enabled to capture 

 its prey. These arms are capable of free 

 movement in every direction, and can be 

 readily retracted when the animal is dis- 

 turbed. They are also armed with minute 

 oval, hollow cells, each of which has a 

 slender filament coiled up into a spiral 

 within its cavity. Each filament is 



capable of being suddenly protruded, thus becoming a free whip- 

 like appendage, and these are so numerous as to be very effectual 

 in seizing and holding the living beings on which the animal 



Fio. 77. THBEAD CELLS 



OF A CCELENTERATE, 

 MAGNIFIED 



1. Thread retracted 



2. Thread protruded 



