COPEPODS OF LAST CRUISE OF CARNEGIE 



of silk bolting-cloth of size lo(XXX), and the lower section 

 2.0 meters in length of size I5(XXX). 



Localities 



Tows were taken at each of the i(>2 stations designated 

 on the accompanying map (map i), though tows at only 

 15S regular stations were considered.' Enough others were 

 taken between the stations to bring the total of the 

 localities up to 208. Not including 3 localities in the 

 North Sea, only 39 of these localities are in the Atlantic 

 Ocean, the remaining 166 being in the Pacific Ocean. As 

 a result the Pacific is well covered from 52° north latitude 

 to 40° south latitude, but in the Atlantic the stations are 

 all north of the equator. This disparity was not inten- 

 tional, but was due to the unfortunate destruction of the 

 Carnegie at the close of the first half of her cruise. The 

 second half of the cruise had been planned to include the 

 southern part of the Pacific between 40° and 60° south 

 latitude, the South Atlantic from the equator to 60° 

 south latitude, and the entire Indian Ocean. This would 

 have furnished data of supreme value for a comparison 

 of the plankton of the three oceans. It is fortunate that, in 

 accordance with the Carnegie's rule to forward imme- 

 diately to Washington at each port of call all accumulated 

 data and collections, no data or plankton collections were 

 lost at Samoa in the destruction of the vessel. 



Depth of Tow 



At each of the regular stations three tows were taken, 

 one at the surface, a second at 50 meters, and a third at 

 100 meters. The second and third nets were attached to 

 the same wire; the surface net was on a separate wire, 

 but was towed simultaneously with the other two. All 

 the nets were drawn horizontally for a sufficient distance 



to obtain an excellent sample of the plankton at each of 

 the three depths. The length of the tow varied consider- 

 ably and is recorded for the Pacific stations only (pp. 42- 

 168). All the tows between the regular stati(jns, with one 

 or two exceptions, were taken at the surface only when 

 the vessel slowed down sufficiently or was becalmed. No 

 vertical tows were made, with the single exception of one 

 at station 64, and this was also the only one below 100 

 meters in depth. 



Time oh Tow 



All the tows at the regular stations were started at 8''3o'" 

 A.M. local mean time, the time of completion varying 

 with the length of the tow. Thus they were all daylight 

 tows taken at about the middle of the forenoon, and none 

 taken during the afternoon, evening, or night. This regu- 

 larity of the time of the tows adds greatly to their value 

 for purposes of comparison. 



The surface tows between stations, being dependent 

 on the slowing down or becalming of the vessel, never 

 came regularly but were taken at any time during the 

 twenty-four hours, most often at night. They thus supply 

 valuable data with reference to the migration upward of 

 certain species of copepods during the night. 



Volume of Tow (Paciitc Stations Only) 



The volume of the tow was computed by allowing it 

 to settle to the bottom of the bottle and measuring its 

 depth. However deficient this method may be with refer- 

 ence to the actual bulk of the plankton, it does supply a 

 reliable basis of comparison when followed uniformly. 

 When considered in connection with the length of the 

 tow, it furnishes an accurate estimate of the comparative 

 richness of the plankton in any locality. 



QUALIFYING CONDITIONS 



Nets 



It is stated above that the nets used in the 50- and 100- 

 meter tows could not be closed while being lowered and 

 raised. In other words, these two deeper tows were not 

 exclusively horizontal, but included also a vertical or 

 diagonal tow to the surface. This means that copepods 

 could get into them at levels nearer the surface than the 

 recorded depth of the tow. 



In all probability such intrusion of individuals from a 



' For stations 129, 131, 161, and 162, apparently Dr. Wilson clitl 

 not find any material for this report. — En. 



different level actually occurred more or less frequently. 

 But the percentage of these aliens is small, as can be seen 

 by the number of species in each station list recorded 

 exclusively from the two upper levels. Any species con- 

 fined to the 50- or 100-meter level would not be affected 

 by other species coming in from higher levels. But if even 

 one or two specimens of a species which was really con- 

 fined to the surface got into the 50- or the lOO-meter net, 

 it would indicate the presence of that species at a level 

 where it did not really occur. The comparatively small 

 percentage of species found at all three levels and the 

 comparatively large percentage of species confined to a 



