ALTERNATION OF GENERATIONS 253 



gametophyte but to the sporophyte. Thus there is a regular 

 alternation of sporophyte and gametophyte generations such 

 as is not found in any animal. At the same time either the 

 sporophyte or gametophyte generation (more rarely both) 

 in a plant is capable of vegetative multiplication of its 

 members, multiplication being effected by a process of bud- 

 ding analogous to that of the Hydroid stocks. And in many 

 plants members produced by vegetative multiplication may be 

 detached from the parent and grow into independent organ- 

 isms just as the buds of a Hydra are detached and grow into 

 independent Hydrse. Now, the process of budding in Hydra 

 and Obelia is clearly a process of vegetative multiplication, and 

 it is quite open to us to consider a composite stock resulting 

 from this process as an individual body of which the so-called 

 persons, the hydranths, blastostyles, and medusa, are the 

 members, just as the parts of a plant, the leaves and floral 

 organs, are regarded as the members of the individual plant 

 body. On such a view the medusae set free from a Hydroid 

 stock would be regarded as the analogues of the gemmae and 

 bulbils set free from so many plants, and we should apply the 

 term "individual" not to the various members of the stock 

 but to the whole aggregate of members, whether united or 

 detached, which have been produced by the continued growth 

 of the fertiUsed egg. In this case it would not be possible to 

 speak of an alternation of generations in Obelia and its allies ; 

 for it would be absurd to speak of a part of an individual as a 

 generation : and if we limit the term individual to the totality 

 produced from the egg, and consider, as we must, that "indi- 

 vidual" and "generation" are convertible terms, then there is 

 only one generation in Obelia, and that a sexual one. 



Whilst zoologists still hold to the opinion that a hydroid 

 colony is a composite made up of many individuals joined 

 together, and therefore is polymorphic and exhibits alternation 

 of generations, it is by no means clear that the opposite view 

 of the individuality of the so-called colony is not preferable. 

 It is certainly more consistent with the conclusions arrived at 

 by a discussion of the theory of individuality. It is not 

 possible here to enter into the very complicated arguments 

 arising out of the question, What is an individual? But the 

 only answer which does not quickly land us in contradictions 

 and absurdities is the one given by the late Professor Huxley— 



Digitized by Microsoft® 



