COPEPODS GATHERED BY ALBATROSS—WILSON 149 
course, the kind of nets employed and the methods used in collecting 
the plankton have changed considerably, but the results obtained pre- 
sent certain facts and considerations of great interest. 
Of the 472 valid species enumerated in the present report, 12 appear 
in all five of the compared lists, 30 are present in four of the lists, 
79 in three of them, 114 in two of them, and 145 in at least one of them. 
This leaves 93 species found only in the Albatross plankton, of which 
29 are new to science. The 12 present in all the lists may reasonably 
be regarded as the most widely distributed and the most stable of 
the plankton copepods. It sometimes happens that one of these 
species runs amuck at breeding and comes to constitute practically 
the entire bulk of the plankton over a considerable area. Anomalocera 
patersoni, Calanus finmarchicus, Fuchaeta marina, and Undinula vul- 
garis often swarm in sufficient numbers to color the sea in which they 
are swimming. 
On the other hand, the 93 species confined to the Albatross plankton 
constitute just about 19 percent of the total number of species taken 
by the Albatross and may be regarded as the least widely distributed 
and the most transitory of the copepod species in the plankton. They 
do not occur in large numbers, usually two or three specimens in a 
given locality. With the preceding group, they form one of two 
plankton extremes; together they include a little more than one-fifth 
of the entire number of species. 
For the bulk of the plankton the superabundance mentioned above 
is generally temporary, soon disappearing, while the members of this 
last group or extreme never reach sufficient numbers to make them 
worthy of more than honorable mention. It is, therefore, the re- 
mainder, approximately four-fifths of the whole number of species, 
that contributes most to the maintenance of the general average of the 
plankton. Conversely, the two groups forming the extremes of 
abundance are chiefly responsible for the inequalities noted in the 
plankton at different times and in different localities. 
Seventy percent * of all the Albatross plankton was taken in hori- 
zontal tows at the surface, and the same is true of 73 percent of the 
Siboga plankton. In the Monaco plankton 64 percent of the collec- 
tions studied by Sars came from the surface, and of the 512 collections 
examined by Rose only 9 were taken below the surface. In the Wilkes 
and Challenger expeditions no depth statistics are given, but Brady’s 
report begins with this sentence, “The copepods noticed in this report 
were taken almost entirely from surface-net gatherings made during 
8 [The percentages given, as well as the statistical remarks made here and elsewhere in 
the report, are in the main correct. It is not believed that the few species added to the 
manuscript or that the several stations omitted will make any appreciable difference in 
Dr. Wilson’s conclusions.—W. L. S.] 
