1912] Esterly: Copepoda of the San Diego Region 337 
15) that the plurimum is at 75-50 fathoms for the day, though 
the animals were taken in a few more than half of the hauls at 
that level, while from 150-250 fathoms all of the twelve hauls 
were suceessful. At night there are two plurima, at 10-15 and 
at 30-25 fathoms. 
(d) All the nets agree in indicating that there is an upward 
migration at night, though this is shown more clearly with the 
surface and horizontal closing nets. 
(e) The animals appear to leave the surface before the hght 
inereases at all in intensity. This suggests that decreasing hght 
is not the cause of the downward movement. A more complete 
discussion of this question will be found in my paper mentioned 
in (b) above. 
8. In regard to the distribution of Hucalanus elongatus, the 
next most abundant species, we found: 
(a) With the surface net (tables 21 and 22 and fig. 2) that 
the animals are more abundant at night; that the highest average 
per hour for any two-hour period is between 8 and 10 p.m., 
though the number per hour for the six hours of the night before 
midnight is much smaller than for the six hours after midnight ; 
that there are three plurima for the occurrence of the species on 
the surface (fig. 2), in the afternoon, evening and morning. On 
the whole, the occurrence of Hucalanus is erratic, as compared 
with that of Calanus. 
(b) With the Kofoid horizontal closmg net we found that 
there is an extensive movement of the species from a day pluri- 
mum at 200 fathoms, which does not seem to come under the class 
of diurnal migrations (Esterly, 1911a). 
(c) With the vertical closing nets we found (tables 23 and 
24) that the day plurimum is probably at 200 fathoms as an 
average depth; that the abundance and frequency above 50 
fathoms are greater by night than by day, while below 50 fathoms 
the reverse is the case. 
9. The distribution of Metridia lucens shows the following 
features : 
(a) With the surface net (tables 26 and 27) the greatest 
abundance and frequency is between 10 p.m. and 2 a.m.; that 
the hourly average is enormously larger between 10 and 12 p.n., 
