624 REPOKT OF COMMISSIONER OF FISH AND FISHERIES. 



isms iu single regions of currents, and lias twisted it in favor of bis 

 theory of the regular distribution of the ])lanMon: 



The tests of the volume of the plankton show that, five times in the north, once 

 north of Ascensiou, extraordinarily laryv catches ( !) were made. These must have been 

 caused by various currents in this regiou, and can therefore be left out of consider- 

 ation (9, p. 249). 



It seems to me that Hensen would have done better to take into 

 consideration these Jind other facts observed by him relative to the 

 unequal plankton distribution before he built up his fundamental, 

 certainly adequate, theory of the equality of the same. This was to be 

 expected, since he himself in his first oceanic plankton studies (1S87) 

 observed mauy 'h'emarliahle inequalities,'^ mid his own tables furnish 

 l)roof of this. While he many times mentions the immense swarms of 

 Medusw and declares this " quite superabundant accumulation to be 

 mysterious," he adds: "such j)lacesmust be avoided in this fishery" (9, 

 pp. 27, 65). When Hensen later, in comparing the different catches of 

 copepods (one of the most important planktoiiic constituents), finds 

 that the distribution of the plankton' in tlic ocean is very irregular 

 and that the constitution of this seems to very strongly contradict 

 his general conceptions of natural life (9, p. 52), he holds it to be best 

 that these catches, which are of "such a different kind, should be 

 excluded from consideration" (pp. 51, 53). Also, in the case of Sagitta, 

 which Hensen reckons with the copepods as belonging to the uniform 

 perennial plankton, he finds "throughout not the equality which one 

 might exx^ect, but much more remarkable variations" {]}. 59). 



These "surprising inequalities," "variations even to tenfold," he finds 

 iu case of the Dax)hnid(v (pp. 54, 56) and Hyi^eridw (p. 57), the pelugic 

 larvpe of snails and mussels (pp. 57, 58), Appendicularia and Salpa 

 (pj). 63, 64), the Medusm and Ctenophores (64, 65), the Tintimioids (p. 

 68), the Peridinia^ (!>. 71), and even in the Diatoms (p. 82) — in brief, 

 in all groups of pelagic organisms which by the numerous production 

 of individuals are of importance for the plankton and upon which 

 Hensen employs his painstaking method of calculation by quantitative 

 planktonic analysis. If one freely "sets apart from consideration" 

 all these cases of remarkable inequality (because they do not fall in 

 with the theoretically X)i"econceived ideas of the equality of planktonic 

 composition), then finally the latter must be proved by counting. 



Bathycurrents or deep streams. — Through recent investigations, par- 

 ticularly of Englishmen (Carpenter, Wyville Thompson, John Murray, 

 et al.), we have become acquainted with the great importance of the 

 submarine currents or deep streams. It has been demonstrated that 

 the epicurrents, or the surface streams, furnish us no evidence rela- 

 tive to the understreams to be found below them, which we name bathy- 

 currents. These undercurrents may in different depths of the ocean 

 have a quite different constitution, direction, and force from the over- 

 currents. This is as true of the great oceanic as of the local coast cur- 

 rents. If the more accurate study of marine currents is a very difficult 



