336 University of California Publications in Zoology |Vou.9 
4. This fact of constant change appears to make it doubtful 
if there are regions in which species may be said to be isolated. 
At any rate the data available from the records of this station 
do not show that the abundance of any of the species is related 
to temperature or salinity. These have been taken for the sur- 
face hauls only, as yet, and the species of Copepoda that we 
know most about reach the plurimum at the surface at night 
regardless of the temperature or salinity within the limits known 
for the region. 
5. On the other hand, no two of the curves of distribution at 
the surface with regard to time are the same, so far as the more 
abundant species are concerned. This fact suggests that, just as 
there are structural differences between the forms, there are also 
other characters that mark a species as a definite kind. It is 
also to be suggested that, though two forms may be closely allied 
structurally (so far as we can judge), and taken repeatedly in 
the same area, the other differential characters will show that 
the forms in question oceur coincidently as widely separated 
species. 
6. Ten species have been taken at the surface in large enough 
numbers for judging as to when during the night they reach 
their maximum abundance. Three species do so between 6 and 
8 p.m., five between 8 and 10 p.m., one between 10 and 12 p.m., 
and one between midnight and 6 a.m. (table 55). 
7. Calanus finmarchicus is the commonest species in the San 
Diego region. The following conclusions as to its distribution 
and behavior appear to be well grounded: 
(a) With the surface nets (tables 12 and 13 and fig. 1) we 
found that it is most abundant during the night, between 10 and 
12 p.m., though there is a very marked increase in abundance 
beginning at 6 p.m. After midnight there is a great decrease in 
the size of the hourly averages. 
(b) With the Kofoid closing net we found (Esterly, 1911b, 
tables 4 and 5) that the day plurimum is at 200 fathoms; that 
the evening plurimum is at 100 fathoms; that at midnight the 
plurimum is at 5-10 fathoms; and that from 4 to 6 a.m. the 
plurimum is again at 100 fathoms. 
(c) With the vertical closing nets, we found (tables 14 and 
