1912] Esterly: Copepoda of the San Diego Region 325 
It can be seen in the preceding table that there are only three 
exceptions to the rule that the abundance at the surface is greater 
at night; these are, Gaidius pungens, Pleuwromamma quadrungu- 
lata and Scolecithrix persecans. There are only nine animals 
involved for the three species and they are evidently individual 
exceptions, for each species is typically resident in deep water. 
Eucalanus elongatus in both sorts of closing nets and Rhincalanus 
nasutus and Pleuromamma gracilis in the horizontal nets were 
found less abundantly by night than by day above 100 fathoms; 
the other sixteen species were more abundant by night in the 
epiplankton. The species occurring at all below 100 fathoms 
were much more abundant there by day than by night, with the 
exception of Metridia lucens in the hauls with the horizontal 
closing nets. 
It may be pointed out that, though the number of night hauls 
at the surface and above 100 fathoms is smaller than the number 
of day hauls, the number of animals is much larger at night at 
both levels. This makes it unlikely that the larger number of 
animals during the day at or below 100 fathoms is due to the 
larger number of day hauls. 
The Copepoda appear to behave as do the Ostracoda as shown 
by Fowler (1909). He found that out of about fifteen species, 
nine showed an increase in the epiplankton at night, and three 
were never taken at or above 100 fathoms by day; one species 
was taken there once, another was taken twice. Six species did 
not show such a variation by day and night. Table 54 shows 
that out of nineteen species of copepods, six were never taken 
at the surface nor above 100 fathoms by day. There are fewer 
exceptions among the copepods to the rule of increased numbers 
in the epiplankton at night. 
The facts regarding vertical distribution of the copepods of 
the San Diego region show, I believe, that each species is in a 
state of chronic movement as claimed for the ostracods by Fowler 
(1909, p. 299). The reasonable explanation of increased 
abundance at night above 100 fathoms is that the population is 
actually augmented by specimens coming up from below, especi- 
ally since there is a decrease in the numbers of animals taken 
below 100 fathoms at night. The idea that we have to deal with 
