1912] Esterly: Copepoda of the San Diego Region 335 
advanced any views that I regard as more than tentative, 
although the data as analyzed lend strong support to the sugges- 
tions that have been made. Michael has well expressed my feel- 
ings in his concluding paragraph (p. 160) as to proving con- 
clusions. I feel as he does, also, in regard to the necessity of 
improving our methods of collecting, especially as to the use of 
similar nets at all depths. From my experience up to this point, 
I feel that one suecessful haul with the Kofoid net is more 
valuable than many with the vertical nets. We need, also, more 
hauls of that sort at night and especially between 25 and 150 
fathoms; day and night hauls at 200 fathoms and below would 
also tend to clear up some obscure points. 
I wish to express my appreciation of the many favors ex- 
tended to me by Professor W. E. Ritter, Director of the La Jolla 
station, and by Mr. E. L. Michael, the Resident Naturalist, and 
particularly of the friendly and helpful conversations with them 
My wife has patiently helped in the tiresome drudgery of making 
tables and checking results; hers is no small part in that portion 
of the work. 
SUMMARY 
1. The Copepoda as a group are found mainly in deep water 
during the day, the upper limit being not above 150 fathoms; 
the region of greatest abundance on the whole is probably about 
250 fathoms. 
2. It is the rule, practically without exception, that the 
abundance is greater at higher levels during the night than 
during the day, and that such deep water forms as come to the 
surface do so mostly at night. In other words the epiplankton 
is more populous at night, the mesoplankton during the day. 
3. Thus there seems to be a constant oscillation of these 
Crustacea, there being a day and a night plurimum or ‘‘center 
? 
of migration.’’ If we may take it for granted that the region 
of greatest abundance is located where the largest number of 
optimum conditions are found, the fact of diurnal movement 
suggests that the optimum is a rather indefinite term since it 
changes with the time of day. 
