4 



single leve 



ire good proof ilial tlie mixing of different 

 levels was rare. The relative abundance of any species at 

 different levels will also prove helpful in deciding where 

 it really belongs. For example, suppose a species is suffi- 

 ciently abundant at the surface to constitute 80 or 90 per 

 cent of the surface tow, as sometimes occurred, and only 

 one or two specimens are found in the tows at lower 

 levels. It is reasonable to infer that the latter specimens 

 do not really belong to the deeper tow, but entered while 

 the net was being raised or lowered. There will neces- 

 sarily be some mixing of levels, but it is so slight as to be 

 practically negligible, and none of the important results 

 here considered is at all affected by it. 



Depth ok Tow 



Since the lowest depth at which tows were taken (with 

 one exception) was 100 meters, whereas the depth of the 

 bottom at all but 5 of the stations ranged from 2000 to 

 8000 meters, it follows that the entire towing was prac- 

 tically at the surface. We are concerned here, therefore, 

 with the epiplankton exclusively, and not at all with the 

 bathyplankton. This means that the range of the species 

 here recorded must be regarded as essentially a surface- 

 area distribution, and only incidentally as a depth distri- 

 bution. This consideration is of special importance in 

 comparing the present records with those of other expe- 

 ditions, notably the Challenger, Siboga, and bathypelagic 

 Monaco expeditions. It is obvious that none of the 

 numerous rare and often unique species obtained at 

 depths ranging from several hundreds to even thousands 

 of meters can be expected in these surface tows. Their 

 absence from these records, therefore, is no indication 

 that they were not present at the localities examined, but 

 simply that the nets did not descend far enough to 

 secure them. On the other hand, the presence in these 

 tows of certain species obtained by other expeditions in 

 vertical tows starting from considerable depths shows 

 that such copepods cannot be regarded as exclusively 

 bathypelagic. 



The Siboga expedition yielded the largest total of 

 species thus far recorded. But at every station of that 

 expedition whose record of species totaled above 70, the 

 towing was done with a Hensen vertical net starting 

 from depths of 700 to 2000 meters. These same deep ver- 

 tical tows included most of the new species that were 

 obtained. In view of these considerations, the facts that 

 the Carnegie stations from 35 to 44 inclusive averaged 83 

 species, and that several other stations yielded species 

 totals of from 90 to over 100, assume a greatly enhanced 

 significance. These facts should be kept constantly in 

 mind also when comparing the Carnegie records with 

 those of the Challenger, Siboga, and Monaco expeditions. 



COPEPODS OF LAST CRUISE OF CARNEGIE 



SUPI'LEMEN'TARY DaTA 



In the station lists of species herewith presented there 

 arc included statistics regarding certain factors which 

 have considerable significance in copepod distribution. 



The Carnegie Institution of Washington has furnished 

 the author with blueprint lists showing the temperature, 

 salinity, density, and hydrogen-ion concentration of the 

 sea water at the three tow depths for each station. These 

 data are reproduced here, but those pertaining to condi- 

 tions of the weather, sky, and sea at the various oceano- 

 graphic stations are not given in this report inasmuch as 

 they are to be published in other volumes of this series 

 giving the observed data and discussions relating to 

 physical oceanography and to meteorology. A second 

 blueprint list supplies for the Pacific stations (35 to 162) 

 the total volume of the plankton for each of the tows and 

 the distance through which the net was drawn to secure 

 that volume. The data for volume and distance are not 

 available for the 34 Atlantic stations except in one or two 

 instances. 



The lists of copepod species from the three tows at 

 each station have been kept separate, and there is also 

 recorded the comparative abundance of each species at 

 the three depths. 



All these data are incorporated in each station list be- 

 cause it is believed that they are fully as valuable as the 

 lists of species themselves. As far as is known, such data 

 have never before been presented in connection with 

 station lists. They furnish practically all the information 

 that can be obtained with reference to each locality. 

 Without them the list is devoid of any information ex- 

 cept the mere names, and becomes practically meaning- 

 less. 



Oceanic Currents 



The surface currents of both the Atlantic and Pacific 

 oceans were fairly well known and had been charted 

 before this cruise of the Carnegie. The observations taken 

 during the present cruise confirm previous discoveries 

 and add a great many of the missing details. Very much 

 less is known about the deep-sea currents, but since all 

 the Carnegie tows were confined to the upper 100 meters 

 of water, these deeper currents would not affect them so 

 much as would those at the surface. The thing that con- 

 cerns us most in dealing with the copepods is the evi- 

 dence of an intimate relation between the surface cur- 

 rents and plankton distribution. 



The only surface current of any importance in the 

 North Atlantic is the well known Gulf Stream. This was 

 crossed several times by the Carnegie, and its influence 

 was chiefly manifested in an increase of the copepod 

 plankton, both in species and in numbers. There were 



