5 i4 DISCOVERY REPORTS 



a most thorough investigation; for if they are true then all naturalists who many years previously, 

 and in the most extensive compass, have studied the composition and distribution of the plankton 

 are completely in error and have arrived at entirely false conclusions. If, on the other hand, these 

 propositions of Hensen are false, then his entire plankton theory based thereon falls, and all his 

 painstaking computations are utterly worthless. 



Few will deny the great importance of the work of Hensen and his school in the 

 development of planktology. It was a pity that Haeckel's attack was so bitter and that 

 he did not confine his criticism to the question of irregularity in distribution ; as is well 

 known he disputed also one of the most important conclusions of the work of Hensen's 

 Plankton Expedition : that the plankton is on the whole more abundant in the colder and 

 temperate regions than in the tropical seas. Since Haeckel's views on this latter question 

 were shown to be in error, and it was clear that he had misunderstood some of Hensen's 

 other conceptions, his remarks on the uneven distribution of the oceanic plankton lost 

 much of their force. 



The records of plankton described in the present paper were taken in the open ocean 

 during the voyages of the R.R.S. 'Discovery' and R.R.S. 'William Scoresby' in the 

 years 1925-7 with the original form of Continuous Plankton Recorder (Hardy, 1926, 

 1936). They were made with a view to studying the main fluctuations in the planktonic 

 density along uninterrupted lines of observation. These lines varied from 23 to over 100 

 miles in length and were made in different oceanic regions from the Tropical to the 

 Antarctic Zone. The recorder, the first of its kind, was far from perfect, and frequently 

 the mechanism broke down from one cause or another; but, in all, satisfactory records 

 were obtained covering a total distance of some 2300 miles. The positions of these 

 records are shown in the chart in Fig. 1 ; they were taken at a depth of between 20 and 

 30 m. 



Whilst quantitative estimates were made, the time available for analysis on the voyage 

 was limited and necessitated broad treatment. The work is intended as a preliminary 

 exploration of the field : to determine the extent of the fluctuations that may be expected 

 in the plankton of different ocean areas and the type of fluctuations found in the main 

 planktonic groups of animals. Only rarely was analysis carried to specific identifications ; 

 usually the fluctuations are expressed in terms of numbers of total Chaetognatha, 

 Copepoda, Euphausiacea, etc. The silk gauze used throughout had 60 meshes to the 

 inch, so that only the larger species of phytoplankton were taken when very abundant. 



The working of the Continuous Plankton Recorder and the method of examining the 

 samples obtained have already been described in detail (Hardy, 1936), but for con- 

 venience may be summarized briefly as follows. When towed, the planes on the machine 

 make it descend to and remain at the required depth, which is governed by the length 

 of the towing line. The water to be sampled flows through a tunnel in the machine, and 

 as it does so a long banding of silk gauze, graduated in numbered sections, winds across 

 the water stream, sieves out the plankton and rolls it up section by section in a pre- 

 servative chamber. The gauze banding is driven across the water tunnel by the action 

 of a propeller in the passing water outside. The distance travelled by the machine is 



