284 University of California Publications in Zoology |Vou.9 
in hauling at night. From table 12, lines 8 and 9, it is evident 
that Calanus is found in greatest abundance at the surface 
during the four hours preceding midnight; this is a fact without 
taking account of the possible factors that operate to produce 
the result observed. It seems very likely that this general con- 
dition is due to diurnal migrating. In column F of table 12 the 
lowest hourly averages are in lines 3 and 4, which inelude the 
two hours before and after midday. In the afternoon and 
evening up to midnight (lines 5—9) the averages increase, after 
which there is a sharp drop in the numbers per hour. It should 
be noted that the highest frequencies are obtained in night col- 
lecting (columns G, H, lines 7-11) during the hours when the 
animals are most abundant. The number of hauls from 8 a.m. 
to 4 p.m. is relatively small, but there is certainly some signifi- 
cance to the facet that every haul made during those hours took 
the animals. It is noticeable that when the hourly average is 
higher the frequencies may be lower and vice versa (ef. columns 
F, G and H, lines 4 and 6). 
Michael (1911, p. 116) found this to be true, also, and has 
given a discussion of possible reasons for it. I cannot add to 
his discussion, but the general facts of distribution are beyond 
dispute both as regards Sagitta bipunctata and Calanus fin- 
marchicus. 
The following propositions may be regarded as well estab- 
lished by the data in tables 2 and 13: 
1. As the light increases during the morning the averages 
per hour decrease. 
2. As the light decreases toward evening the hourly aver- 
ages increase up to a certain time, after which they decrease. 
(See fig. 1). 
At this point it should be noted that following the mght 
maximum the decrease in abundance begins before the lght 
increases; this matter was brought out in a former paper (Hs- 
terly, 1911b) but is a good deal more evident now on the basis 
of a much larger number of hauls. The conclusion from this 
is, evidently, that an inerease in the intensity of light is not 
the only cause of the downward movement from the surface. 
