292 University of California Publications in Zoology \Vou.9 
misleading in that it does not clarify matters. The data concern- 
ing distribution and temperatures are given for what they are 
worth; they do not seem to show that temperature is important 
in determining the distribution of Calanus at the surface. 
There is doubtless a temperature that may be ealled usual at the 
region of maximum abundance during the day, but there is 
no evidence that Calanus seeks that depth because of the tem- 
perature. In view of the movements performed by the species, 
it is difficult to imagine the part that temperature really has 
in the life of these animals. The bulk of the population 
periodically leaves a region where the temperature is about 
9 degrees on the average and moves into water where the aver- 
age temperature is about 17 degrees. The temperature does 
not vary periodically or constantly enough to lead us to consider 
its changes as the causes of the migrations, and it is very 
probable that there is some other cause. The variations in 
the intensity of light are both constant and periodical, and 
it is my belief that light is the primary cause of the movements 
of this species and also the main factor in determining its 
vertical distribution. 
Distribution with regard to salinity—The salinity is known 
for 71 surface hauls made in June, July, August and September, 
and these hauls alone will be considered because of the desir- 
ability of eliminating seasonal changes. This number of hauls 
is rather small, but table 19 will give some idea of the abundance 
of animals at certain salinities and times of day. 
