SEA-FISHERIES LABORATORY. 341 



Again, the species represented in both hauls of a pair 

 are often present in very different numbers. For example, 

 on August 6th, '09, at the mid-channel station, when the 

 Hansen net was hauled twice from 60 faths. to the surface, 

 one haul had 6,420 Copepod nauplii, the other only 300. 

 On August 7th, '09, at the same place, with the ISTansen 

 net hauled through 60-40 faths., one haul had 15 Oithona 

 and 17 Microcalanus, while the other had 2 and 1 respec- 

 tively. On August 17th, '08, in mid-channel, when the 

 Nansen net was hauled from 60 faths. to the surface, one 

 net had 6,250 Ceratium furca, the other only 750. It is 

 thus evident that, even leaving out of the question 

 organisms too small to be retained by the net, a given 

 vertical haul cannot be regarded as necessarily offering a 

 true picture either of the number of species present or of 

 their relative amounts. 



Further evidence of this may be got from considering 

 the following series of hauls through different depths, 

 using the same net : — 



On April 24th, '08, at Stat. I, the Nansen net hauled 

 from 20 to 10 faths. contained 11 species not present in 

 the same net hauled from 20 faths. to the surface (e.g., 500 

 Ceratium tripos), and of the 19 species common to both, 

 the net hauled through 20-10 faths. had the larger 

 numbers in 15 cases, e.g., 30,000 Chcetoceros sociale to 250, 

 and 20,000 Chcetoceros teres to 1,200. 



On September 14th, '08, at Stat. IV, the Nansen net 

 was hauled from 10 to 5 faths., and from 10 faths. to the 

 surface. The 10-5 faths. catch had 9 species not present 

 in the other, and had more of all the species common to 

 the two except in the case of Oikopleura. 



On August 7th, '09, in mid-channel, the following 

 hauls were made with the Nansen net: — 10-0 faths. 

 (twice), 20-10 faths. (twice), 40-20 faths. (twice), 60-40 



