152 University of California Puhlications in Zoology. ["Vol.8 



species is found less abundant above and more abundant below 

 40 fathoms during the day. While the data do not prove 

 nocturnal migration toward the surface they indicate that such 

 migration occurs. 



Of the 94 specimens ol)tained with vertical closing nets one 

 was taken from between 50 and 75 fathoms, five between 75 and 

 100 fathoms, seven between 100 and 150 fathoms, 33 between 

 150 and 200 fathoms, 26 between 200 and 250 fathoms, and 22 

 between 250 and 300 fathoms. Expressing these numbers accord- 

 ing to unit distance of haul they are 2, 11, 7, 36, 33, and 55. 

 (In this instance, in order to avoid fractions of animals, 500 

 instead of 50 fathoms is considered as the unit distance of haul.) 

 The freciuencies corresponding to these numbers are 11, 33, 30, 

 66, 75, and 60. This means that the species did not occur above 

 50 fathoms, and that it increased in abundance from two in 

 50-75 fathoms, to 55 in 250 to 300 fathoms, and in frequency 

 from 11 in 50-75 fathoms to 75 in 200-250 fathoms. 



When vertical closing net hauls are segregated with respect 

 to day and night, it appears that only one specimen was obtained 

 at night. Now we learn from table 56 that the number of night 

 hauls in each depth was very small. Tliis together with the fact 

 that the total number of specimens was only 94, will possibly 

 explain why the animals were not obtained at night. However, 

 whatever the reason may be. it seems certain, from data concern- 

 ing horizontal closing net hauls, that the absence of the species 

 was not due to light. 



Hence, when all the data are considered, we find that, while 

 the species does not occur abundantly in the San Diego region, 

 the following conclusions are suggested : 



1. The species is typically mesoplanktonic. 



2. It occurs very rarely above 25 fathoms and is most abund- 

 ant and frequent between 200 and 300 fathoms. 



3. It occurs in greater numbers within 35 fathoms of the 

 surface during the night than during the day. 



4. It is very possible that nocturnal migrations toward the 

 surface occur, although their meaning is obscure. 



5. Its center of migration is probably below 200 fathoms. 



