148 



BIOLOGY 



containing hundreds of members, all having arisen from the 

 original by budding. This occurs among the hydroids which 

 are common at the seashore, examples of which are shown in 

 Figures 70, 72, and 73. In such colonies the individual mem- 

 bers are called zooids. 



Polymorphism. In the colonies of hydroids shown in Fig- 

 ure 71 the members of the colony are all alike. It not infre- 

 quently happens, however, that when one of these hydroids 



produces a colony by budding, 

 the members (zooids) assume 



FIG. 70. PARYPHA 



An animal related to Hydra, but forming 

 colonies by budding. 



FIG. 71. ALCYONIUM. AN ANI- 

 MAL RELATED TO HYDRA 

 WHICH FORMS COLONIES 



The individual members, which have 

 arisen by budding, are imbedded in a 

 lime base ; p, one of the members of the 

 colony more highly magnified. 



forms unlike each other. In Figure 72 will be seen a colony with 

 two types of members; one of them possessing tentacles and 

 adapted for feeding, and the other without tentacles but develop- 

 ing the reproductive bodies inside of a case. One of these mem- 

 bers is known as the nutritive zooid, nz, and the other as the 

 generative zooid, gz. In some other types of hydroids the mem- 

 bers which arise by budding assume even a greater variety of 

 form. In the colony shown in Figure 73 there is a complicated 



