1912] Esterly: Copepoda of the San Diego Region 291 
It is plain from table 18 that the highest hourly average 
is obtained at a temperature between 18°1 and 19 (column F, 
line 3), while the frequencies are highest for the highest tempera- 
tures (columns G and H, line 4). In table 17 the averages per 
hour are highest when the temperature is between 1821 and 
19° in two eases out of a possible four (column 6, line 3 in 
sections A and D; so far it may be said that there is an apparent 
correlation between abundance at the surface and that range 
of temperature. This holds for early morning (section A) and 
late night (section D). It is not easy to say whether or not 
the general lack of correspondence between abundance and fre- 
queney is significant. Michael (1911, p. 139) found that these 
correspond rather closely. 
It would seem that if temperature is a very effective agent 
in determining distribution there would be some sort of regu- 
larity in the arrangement of hourly averages with respect to 
temperature; that is, in the present case, we should expect the 
highest average to be at the same temperature whatever the 
time of day. This is obviously not the case in table 17, where, 
in section B, columns 5 and 6, there is a regular series for 
the abundance from the lowest to the highest temperatures. 
The order of abundance in relation to temperature varies in 
all the sections of the table. If table 18 is considered from 
all points of view, it is very difficult to discover a constant 
relation between temperature and abundance; the conclusion is 
that this factor within the limits of surface variation revealed 
by our data has but a slight effect, if any, in determining the 
distribution of Calanus, and this conclusion is strengthened by 
the data in table 16. 
It is true that table 18 shows the animals to be least 
abundant at a low temperature and that there is an increase 
in abundance to the maximum at 18°1-19° (columns E and F, 
lines 1-3). This table, however, summarises the distribution 
with regard to temperature without the possible effects of light. 
This is impossible under natural conditions and we know that 
the abundance is much greater at certain times of day than at 
others. It seems to me that the apparent relation pointed out 
between the temperatures 18°1-19° and abundance is_ really 
