THE CGELENTERATA 57 



altered in structure, often losing the power of de- 

 veloping tentacles, and exhibiting other changes. 

 So much are they altered sometimes that they 

 seem to be mere buds, not separate animals at all. 



In other cases a still more surprising thing 

 happens. The bud that is destined to produce 

 eggs falls off, and becomes quite independent of 

 the colony ; more than this, it becomes quite dif- 

 ferent in appearance from the members of the 

 colony : and instead of being a Hydra-like ani- 

 mal it becomes a jelly-fish. But the eggs of this 

 jelly-fish do not produce jelly-fishes : they pro- 

 duce a more or less Hydra-like animal which 

 gives rise by budding to a fresh colony. This is 

 what is known to Zoologists as " alternation of 

 generations." 



Now comes a puzzling question Which part 

 of this family group shall we select and call it an 

 " animal " ? Is each Hydroid of the colony an 

 animal, and the jelly-fish another animal ? Zool- 

 ogists say " No " : from the development of one 

 e &> t the production of another, is the cycle 

 that constitutes an individual animal. So we 

 have the puzzling result in nomenclature, that 

 an "individual" consists of a very large colony 

 of creatures in one place, together with a perfect 

 shoal of creatures quite unlike it, floating miles 

 away from it on the ocean. What name must we 

 give to the units, so curiously connected with one 

 another ? Zoologists call them " Zooids " (animal- 

 like parts) or "persons." 



This is the story of the jelly-fish as originally 

 told. But there are innumerable variations upon 

 it. There are kinds of jelly-fish that produce 

 jelly-fish and have no Hydroid stage at all. 

 Sometimes the "persons" of the colony present 



