302 



DE. G. H. FOWLEE— BISCATAN PLANKTON ; 



The Vertical Diurnal Oscillation of the Epiplankton. 



It is obvious from the account of the separate species already given that many of 

 them were taken in greater numbers by night than by day. It has been urged upon me 

 more than once in connection with other groups that this is an argument, not for the 

 presence of organisms in greater numbers at night, but for their seeing and avoiding 

 the nets by daylight. Such a criticism can hardly apply to the Halocypridae, which 

 have no eyes. 



Fig. L. 



40 A.M. TO 7-D P.M 



70 P M TO 40 A.M 



CURTA 



MAGNA 



A URVAE 



RDTUNOATA 



GLDBOSA CLOBOSA 



Spindles of day and night distribution of five HalocypridiB. 



To what, then, is their capture in greater numbers by night due ? I can see no other 

 explanation than that the population is actually increased by a rise of additional 

 specimens from lower levels. 



If tow-net hauls could be taken simultaneously at every zone every half-hour for the twenty-four 

 hours, it should be possible to trace the gradual increase and decrease in numbers, and it is with the 

 idea of suggesting such an experiment for the next deep-sea expedition that I venture to j)riut this 

 jjaragraph. But the work will demand a large and wakeful staff of naturalists. 



