November 26, 1909] 



SCIENCE 



741 



have since been able to make similar tra- 

 verses of several of the great oceans, in 

 addition to the North Atlantic, namely, 

 twice across the equator and through the 

 South Atlantic, between England and 

 South Africa, and four times through the 

 Mediterranean, the Eed Sea and the Indian 

 Ocean to Ceylon; and no doubt other nat- 

 uralists have done much the same. The 

 method is simple, effective and inexpensive ; 

 and the gatherings, if taken continuously, 

 give a series of samples amounting to a 

 section through the surface layer of the 

 sea, a certain volume of water being 

 pumped in continuously through the bot- 

 tom of the ship, and strained through the 

 fine silk nets, the mesh of which may be 

 the two-hundredth of an inch across, before 

 passing out into the sea again. In exam- 

 ining with a microscope such a series of 

 gatherings across an ocean, two facts are 

 brought prominently before the mind : ( 1 ) 

 the constant presence of a certain amount 

 of minute living things; (2) the very great 

 variation in the quantity and in the nature 

 of these organisms. 



[Illustrations showjng this were given.] 



Such gatherings taken continuously from 

 an ocean liner give, however, information 

 only in regard to the surface fauna and 

 flora of the sea, including many organisms 

 of fundamental importance to man as the 

 immediate or the ultimate food of fishes 

 and whales and other useful animals. 



[Examples were shown.] 



It was therefore a great advance in 

 planktology when Professor Victor Hensen 

 (1887) introduced his vertical, quantitative 

 nets which could be lowered down and 

 drawn up through any required zones of 

 the water. The highly original ideas and 

 the ingenious methods of Hensen and his 

 colleagues of the Kiel School of Planktol- 

 ogy— whether all the conclusions which 

 have been drawn from their results be ac- 



cepted or not— have at the least inaugu- 

 rated a new epoch in such oceanographic 

 work ; and have inspired a large number of 

 disciples, critics and workers in most civil- 

 ized countries, with the result that the dis- 

 tribution of minute organisms in the oceans 

 and the fresh waters of the globe are now 

 much more fully knowTi than was the case 

 twenty, or even ten, years ago. But per- 

 haps the dominant feeling on the part of 

 those engaged in this work is that, not- 

 withstanding all this activity in research 

 and the mass of published literature which 

 it has given rise to, much still remains to 

 be done, and that the planktologist is still 

 face to face with some of the most impor- 

 tant unsolved problems of biology. 



It is only possible in an address such as 

 this to select a few points for demonstra- 

 tion and for criticism- the latter not with 

 any intention of disparaging the stimula- 

 ting work that has been done, but rather 

 with the view of emphasizing the difficul- 

 ties, of deprecating premature conclusions 

 and of advocating more minute and more 

 constant observations. 



The fundamental ideas of Hensen were 

 that the plankton, or assemblage of more 

 or less minute drifting organisms (both 

 animals and plants) in the sea, is uniformly 

 distributed over an area where the physical 

 conditions are approximately the same, and 

 that by taking a comparatively small num- 

 ber of samples it would be possible to cal- 

 culate the quantity of plankton contained 

 at the time of observation in a given sea 

 area, and to trace the changes of this plank- 

 ton both in space and in time. This was a 

 sufficiently grand conception, and it has 

 been of great service to science by stimu- 

 lating many workers to further research. 

 In order to obtain answers to the problems 

 before him, Hensen devised nets of the 

 finest silk of about 6,000 meshes in the 

 square centimeter, to be hauled up from 



