THE SCHIZOPODA. 



123 



On the question of a vertical oscilhition, as Messrs. Holt and Tattersall have already 

 pointed out (p. 109), the table on p. 118 seems to indicate a nocturnal rise and diurnal 

 fall of this species. But it seems worth while to present the evidence for this view in 

 the form of statistical tables in the same manner as has been adopted for Sagitta 

 serratodentata (p. 60), a case in which the reverse oscillation appeared to hold good *. 

 The following table shows the average catch per hour haul by " day " and " night " ; 

 the dawn, about 3.0 a.m., and dusk, about 7 p.m., are the most convenient dividing hours ; 

 but if J..0 A.M. be taken instead of 3.0 a.m., allowing time for the species to sink after 

 dawn, the contrast is even more marked, and the method is probably more in accord 

 with the facts. 



The arrangement of the captures according to the light-intensity as tested by a 

 photographer's actinometer, which gave no results in the case of Sagitta serratodentata, 

 confirms the idea of the oscillation of Ifiilleri, and indicates that the movement affects 

 the upper 100 fathoms a little before dusk and after dawn. In the next table, whicli 

 illustrates this point, the hauls were arranged according as the actinometer assumed the 

 standard tint at 2", 3"-6", 7"-10", 11" to dusk or dawn ; the remaining: hauls bein"- 



was evidently made under abnormal circumstances, and sends up the values for 50 fathoms in all the tables to 

 a disproportionate extent. My log records " beginning to blow, some rain " about midnight, and it is barely possible 

 that the weather concentrated at 50 fathoms specimens which normally would have been at hin-lier leveh at that 

 hour. The number caught was so abnormiil that tlic haul has been omitted from the tables of E. Miilleri and 

 N. megalops, the values obtained by its retention being, however, recorded in footnotes ; if included in this table, 

 the average specimens at 50 fathoms would be 23-3. 



* As this species, unlike sa-ratodcntata, was only found at the surface at night, and the hauls " during or after 

 rain " were all in daylight, the latter are not shown separately from the rest. 



t If haul 31 b be included, 5 hauls yielded an average of 60-0 ! The single haul at 50 fathoms which showed 

 specimens in daylight was 32a, 4.15 to 5.15 a.m. 



