1918] Michael: Behavior of Salpa democratica 285 



the ensuing discussion partly offsets it. "Witness, for example, the 

 following from page 773 : ' ' Hensen invented his method for the pur- 

 pose of investigating the floating or suspended life in the sea, which 

 he termed 'plankton.' This plankton is, however, very difficult to 

 define, for among the profusion of organisms, ranging from the 

 minutest plants ... to the large crustaceans and fishes, there is an 

 enormous variety in size, in activity, and consequently in the faculty 

 of avoiding the appliances of capture. In many investigations, there- 

 fore, the word plankton may be taken to signify practically 'the catch 

 made in the hoop-net constructed by Hensen, when new and in per- 

 fect working order.' " A further step in the same direction is taken 

 by Fowler (1912, p. 162) in his Science of the sea: "To those animals 

 and plants which float in the sea, whether at the surface or in deep 

 water, the term ' Plankton ' is applied for brevity ; they are contrasted 

 with the creatures which crawl upon, or are fixed to, the bottom. In 

 modern usage. Plankton is generally taken to include even powerful 

 swimmers . . . as well as helpless and minute organisms. " Similarly, 

 under the term "plankton" in the last edition of the Encyclopaedia 

 Britannica, Fowler (1911, p. 720) writes: "Plankton, a name invented 

 by Professor Victor Hensen for the drifting population of the sea." 

 But, in the next column : ' ' The fauna of the sea is divisible into the 

 plankton, the swimming or drifting fauna which never rests on the 

 bottom (generally taken now to include E. Haeckel's nekton, the strong 

 swimmers such as fish and cephalopods), and the benthos, which is 

 fixed to or crawls upon the bottom. ' ' 



Although these statements, quoted from Fowler (1911, 1912) and 

 from Murray and Hjort (1912), represent a decided step in advance, 

 they still carry the implication that a large number of plankton 

 organisms are as helpless as drifting physical particles ; that they play 

 a negligible part in their own distribution. There may be such 

 organisms, but ought this not to be demonstrated rather than assumed ? 



Is it beyond question that even fish eggs are of necessity distributed 

 in accordance with this assumption? At a depth of twenty fathoms 

 two eggs begin development at the same time and place ; the rate of 

 growth is more rapid in one ; it 's specific gravity decreases and it 

 ascends, reaching the surface by the time the second, more slowly 

 developing, egg has ascended to the fifteen fathom level. The surface 

 current flows southward ; that at fifteen fathoms, to the west of south. 

 At the end of two days the two eggs are ten miles apart. Has the 

 difference in their rates of growth played a negligible part in deter- 



