56 THE STORY OF ANIMAL LIFE 



For this reason the group to which Hydro* 

 belongs has received the name of Eleuthero- 

 blastese, the animals with free buds. But Hydra 

 has many near relations in which these buds are 

 not so cast off, but remain attached to the par- 

 ent ; and they in turn may produce others which 

 also remain attached. 



In this way, groups or colonies are formed, 

 consisting of large numbers of individuals, and 

 possessing a common stalk or stock which is 

 formed by degrees as the process of multiplica- 

 tion goes on. The corals and the corallines are 

 familiar examples of this. 



The matter is complicated by the fact that 

 either the separate animals or the flesh of the 

 stock, or both, may secrete within themselves a 

 hard supporting structure forming what is known 

 as Corals. This may be developed in such a 

 complicated manner, that instead of the coral 

 appearing to be the product of the animal, the 

 animal seems to be inserted in the coral, into 

 which indeed it can retract itself for shelter. 



The Corallines, on the contrary, secrete a 

 leathery coating or sheath outside themselves 

 and the stock. The leathery case is fairly trans- 

 parent, so that on magnifying the creature the 

 flesh of the common stock, as well as of the 

 stalks of individual animals, may be seen inside. 

 The " heads " of the animals poke out at the end 

 of each branch (see Fig. 9). 



The Hydra, with which we started, had always 

 the power of producing eggs; each animal could 

 do so, besides producing buds. But in our Co- 

 lonial Coralline this is not necessarily so. Some 

 individuals lose the power of producing eggs. 

 Others can do nothing else, and become greatly 



