82 REPRODUCTION 



many attached individuals that have arisen by budding 

 from a single parent. After a period of this kind of 

 budding, the colony forms other buds of a different shape 

 and structure. When these mature they detach themselves 

 and become free sw^imming jelly-fish. No naturalist, 

 discovering them sw^imming in the water, unless he knew 

 the facts just stated, would ever suppose for a moment 

 that these jelly-fish were in any way related to the colony 

 from which they actually came. The free jelly-fish 

 produces gametes, which unite sexually and form embryos. 

 When the embryos develop they are not like their parents 

 the jelly-fish, but are like their grandparents, the tubular 

 hydroids. They settle down and reproduce by budding. 



Many such instances are found in the coelenterates (that 

 branch of the animal kingdom to which the hydra belongs) 

 and among the parasitic worms, such as liver flukes, tape 

 worms, and the like. 



6. Some Advantages in Alternation of Generations in 

 Animals. We do not know what forces have brought 

 about alternation of generations, but we can see that it 

 may be of some advantage to the organisms having it. It 

 gives a kind of double chance for organisms to scatter and 

 to become adapted to life conditions. For example, in 

 attached forms such as hydroids, the budding enables a 

 single individual that manages to become attached in a 

 favorable place gradually to take complete possession of 

 that spot by budding. Being attached has advantages, but 

 it also has handicaps. If conditions change, the colony 

 may be destroyed. Besides, there is no chance in budding 

 for wide distribution. Now the formation of another kind 

 of individual which is free-swimming, and able to produce 

 eggs and sperms, gives the fixed colony a chance to spread 

 its offspring widely and to seek out many favorable 

 localities for growth. In this way the advantages of both 

 methods are combined in one species. 



In the parasitic form, the alternation is often an aid in 



