182 University of California Publications in Zoology |Vou-9 
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From the information that had been secured by work done 
previous to making the plans here described, it seemed best to 
concentrate still more on the effect of season upon the kinds and 
abundance of organisms. Three localities were selected on a 
line extending approximately west of the south end of South 
Coronado Island. These three localities were taken for the 
following reasons. First, because of the ease with which sextant 
observations may be made in almost any kind of weather. 
Second, because of the bottom topography and its consequent 
hydrographie and biological interest, especially as affording 
opportunity for testing Ekman’s theory of oceanic currents, and 
of determining the effect of upwelling water on the organisms. 
Third, because little time would be consumed in running from 
station to station, and from station to good anchorage, the 
farthest station, although in water having a depth of 700 
fathoms, being within ten miles of the island. 
The locality settled, the question of the time of day when 
work should be done was next considered. It was certain from 
observations already made that some organisms accumulate at 
the surface during morning and evening twilight, and occur in 
deeper water during daylight and darkness. Work ought to be 
done consequently during these four parts of the day. The 
‘* Agassiz’? not being capable of accommodating two crews, work 
could not proceed more than twelve hours each day. Which, 
then, should be the period of work, from noon till midnight or 
from midnight till noon? It was decided to take first the part 
of the day that includes morning twilight mainly from practical 
reasons, such as the disinclination of most crews to run for an 
anchorage during darkness, and the fact that the ocean in this 
vicinity is usually much smoother from midnight to noon than 
after noon. Further considerations concerning the time con- 
sumed in handling the apparatus made it impracticable to work 
each station from surface to bottom, so that either deep water or 
shallow water collecting would have to be left out of this par- 
ticular programme. Resorting again to experience and data 
already secured, it seemed best to work mainly in the upper one 
hundred fathoms. 
