328 University of California Publications in Zoology |Vou.9 
There is only one case (Hucalanus elongatus) where the two 
plurima do not coincide. 
Table 55 shows that three species were at their plurimum 
between 6 and 8 p.m., five between 8 and 10 p.m., one between 
10 and 12 p.m., and one between 12 pm. and 6 am. As to 
totals, the period from 10 to 12 p.m. is overwhelmingly pre- 
dominant owing to one haul of Metridia lucens that contained 
32,000 specimens. The number of hours of hauling between 8 
and 10 p.m. and 10 and 12 p.m. are small compared to the time 
from 6 to 8 p.m. or from 12 p.m. to 6 a.m., but the numbers of 
animals per hour are much larger for the shorter times. This 
is to be expected, but the totals of those times are so high that 
it is to be presumed that the averages would be at least relatively 
as large if there had been more hauls. 
All species do not have the same time of maximum abundance 
at the surface as shown by table 55, but in eight cases out of ten 
it occurs between 6 and 10 p.m. On the whole, there is no reason 
to doubt that table 55 gives an approximately correct idea of 
the time of greatest abundance at the surface for the species 
considered. 
I have been unable to find that there is any clear relation 
between the distribution of the Copepoda of this region and tem- 
perature and salinity of the water. It may be said that the 
expectation was that such a relation would appear, especially 
in view of the results of Michael with the Chaetognatha. This 
investigator is of the opinion (1911, p. 160) that a species is a 
species as much from the physical environment in which it is 
normally found as from its morphological characters. Hjort, 
also (1910, p. 371), states that each of many forms in the same 
area of the sea has its own area of distribution, mode of life and 
habitat, and that a species may be defined by certain conditions 
of existence as well as by its structure. ‘‘These conditions 
characterize a given species quite as much as any morphological 
description, and in fact for a proper conception of the species 
both methods of investigation are supplementary.”’ 
The available data for the Copepoda of this region lend 
plausibility to these views, at least to the extent of showing that 
a species is not characterized by structural features alone. No 
