1914] Esterly: Schizopoda of the San Diego Begion 133 



TABLE 8 ^ 

 Distribution of NycUphanes During the Winter, at the Surface, With Eegard to 

 Different Temperatures, None Above 19? 



Temperatures 

 1. 14° and less 



No. 

 Total 



8 



of hauls : 

 Success. 







No. 

 Total 



7.4 



of hours : 



Success. 







No. of animals: 

 Total Per hour 







Frequency : 



Haul Time 







2. 14?1-15° 



36 



5 



34.75 



4.7 



52 1.5 



14 



14 



3. 15?1-16° 



13 



2 



13.6 



3.1 



19 1.4 



15 



22 



4. 16?1-17° 



12 



5 



13. 



6.35 



418 32.1 



42 



49 



5. 17?1-18° 



2 







1.2 



















6. 18?1-19° 



1 







0.37 



















The results arrived at in the preceding table seem to be worthy 

 of confidence. The optimum temperature for NycUphanes is clearly 

 between 16 ?1 and 17°. It may not be significant that no specimens 

 were obtained in water above 17°, because the hauls are so few, but 

 it may at least be regarded as true that the species is not found at 

 temperatures below 14 ?1 on the surface. 



The effect of salinity on the distribution of the schizopods warrants 

 only brief mention. There are four surface hauls out of a total of 

 135, for which the salinity is known, that obtained Euphausia during 

 the summer. The salinities lie between 33.66 and 33.70, and 177 of 

 the 185 animals obtained during the summer were in those four hauls. 

 It may be suggested, therefore, that the optimum salinity at the sur- 

 face is within the limits mentioned. 



The salinity is given for 22 surface hauls made during the winter, 

 but only one of these hauls obtained NycUphanes; the salinity is set 

 down as 33.61. There were 13 animals in the haul. 



Another factor, in addition to temperature and salinity, that may 

 influence the distribution of organisms at the surface is light. It is 

 possible to gain some idea of the effect of light by comparing the 

 numbers of animals taken at different times of day. In accordance 

 with the plan followed in other papers of this character (Michael, 

 1911, Esterly, 1912), the day is divided into twelve two-hour periods, 

 and the results for Euphausia with regard to the summer hauls are 

 set down in table 9, which follows. 



It will be noted in the table that no animals were obtained from 

 4 a.m. to 6 p.m. (lines 12-6). From 6 p.m. to 4 a.m. there are six 

 successful hauls in 46, with a total of 185 animals. The time of great- 

 est abundance is from 6 to 8 p.m. (line 7). The results do not indicate 

 that there may be a diurnal migration, and our data for the summer 



