326 THE BRITISH NATURE BOOK 



or to extend into a long stalk or column, tipped with a few slender tentacles. 

 This is one of the objects for study with your pocket lens or microscope, 

 and is to be found on duckweed in many a ditch or shallow pool. It is very 

 minute, remember, and will have to be looked for, but is very common. 

 There are three kinds orange-coloured, brown, and green. Their tentacles are 

 studded with suckers capable of paralyzing the water-fleas and other minute 

 creatures on which they live. They multiply by putting out buds, which 

 separate from the parent and start an independent existence of their own. As 

 I have written at some length on these fascinating creatures in The Young 

 People's Microscope Book, I must refer interested readers to its pages. 



But most of the Zoophytes (to use the familiar term literally, " animal- 

 plant ") are marine, and are frequently mistaken for some kind of seaweed 

 from their outward appearance. They are, however, colonies of minute 

 animals (polyps or polypi tes), living not separate lives, but held together by a 

 common " body " known as the ccenosarc generally a living tube of thin flesh, 

 which acts as a trunk or support for the community. Yet though not inde- 

 pendent, each polyp is distinct, and each chamber or cup of the whole zoo- 

 phyte is occupied by one member of the colony. 



Usually the outer wall of the ccenosarc is hard, being composed of chitin 

 the same substance that forms the outside skeletons of insects, and forms a 

 sheath known as the polypary. 



The food caught and eaten by one polyp nourishes the others as well as 

 itself ; for this purpose each has a number of tentacles, in the centre of which 

 is the mouth. 



At certain seasons of the year special polypites are formed, whose business 

 is not to catch food but to produce eggs, which they discharge at last by 

 bursting. Others detach themselves from the parent colony and float away, 

 resembling minute jelly-fish ; but others, it must be added, attain an enormous 

 size, as jelly-fish, so that it is almost impossible to credit their having had so 

 lowly an origin. To repeat a well-used illustration, the jelly-fish Cyanea 

 artica, which has been found with a disc 7 feet in diameter and tentacles 50 

 feet long, is produced from a tiny zoophyte not an inch high. 



Many are to be found living on seaweeds ; and it must be remembered 

 that they are very small. The Sea Oak Coralline (Sertularia pumila) is 

 found quite commonly on the serrated wrack. It looks like a miniature 

 leafless tree about | an inch in height. Under the microscope it is seen to 

 have minute cells, in each of which one of the polypites lives. There are 

 some twenty species of these Sertularians in our British seas. 



The Sea Fir (Sertularia abietina) is an abundant species, often found on 

 old oyster shells, and much resembling a fir tree. Another, even more common, 

 is the Sea Hair Coralline (S. operculata], frequently growing on seaweeds, 

 and from 3 to 6 inches long. It grows in tufts not unlike bunches of hair. 

 The Squirrel's-tail Coralline (S. argentea) is very small, with stiff erect 

 branches, and is the most common of all. 



