i-'i*^l MicJtarl: Beliacior of SaljKi (h niocrafica 287 



there is between a copei)od and a fish egg or diatom. Yet sardines are 

 excluded from the plankton, while everything from a diatom to a 

 jelly fish is included. 



Or consider the matter from another point of view ; the sardine 

 begins its career as an egg; by a gradual and continuous process of 

 growth the successive stages in the life cycle follow : the early embryo, 

 the late embryo, the young larva, the mature larva, the post larva, 

 the adult. Clearly, activity characterizes the individual from egg to 

 adult. At Avhat stage does the sardine cease to be a constituent of 

 the plankton and take its place with the nekton? At what stage does 

 its activity become effective in determining its distribution? It was 

 suggested on page 285, how activity might be effective in the egg. If 

 so, can any differential in the type of locomotion or the degree of its 

 effectiveness be recognized that will justify a distinction between 

 plankton and nekton on that basis? Some say that strong swimmers 

 ])elong to the nekton and that such animals alone are able to make 

 headway against a current. But, how strong is a strong swimmer, and 

 against a current of what velocity must headway be made? Merely 

 to raise this question denotes the artificiality of such a distinction. 

 With equal justification might we not distinguish between tlie plank- 

 ton and nekton of the air, defining the latter as strong flyers capable 

 of making headway against the wind ? 



However, in spite of the artificiality of distinguishing between 

 plankton and nekton, the distinction does have a certain methodo- 

 logical value. Might it not be wise, therefore, to combine the state- 

 ments of Fowler (1911, 1912) and of Murray and Hjort (1912) into 

 a definition somewhat as follows? Marine and fresh water organisms 

 are divisible into two main classes: (1) pelagic organisms, the fauna 

 and flora that do not live upon, or fixed to, the bottom; and (2) hrn- 

 tJios. or the fauna and flora which do live upon, or fixed to, the bot- 

 tom. For practical reasons pelagic organisms are artificially subdivided 

 into two groups: (1) ptanMon, or the sum total of all animals and 

 plants captured by any kind of tow-net or water-bottle; and (2) 

 nekton, the sum total of all animals that escape capture by such 

 means. Does not a statement of this nature serve the purpose of dis- 

 tinguishing the two types of organism, insofar as there are two types, 

 without committal as to whether or not any particular ones play an 

 important part in controlling their own distribution ? 



