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DE. G. II. FOWLEE— BISCATAN PLAKKTON : 



As to the agency, be it mechanical, chemical, or physical, or a combination of these, 

 which appears to bring certain species up at niglit, I have only to remark that the 

 distances which have to be traversed in the time seem too great for Ostwald's explan- 

 ation to be alone adopted for all oceanic species ; besides, it is not the whole oceanic 

 plankton that oscillates (as it should by his theory, except in the case of powerful 

 swimmers) but only certain sj)ecies, if my dedu.ctions are correct. Nothing is more 

 puzzling than the sudden appearance during the dark hours (often in very large numbers) 

 of a species which was seldom or never taken in the epiplankton in daylight during the 

 whole cruise. For example, with the exception of a single specimen at 100 fathoms at 

 mid-day, all the 204 epiplanktonic specimens * of daphnoldes were captured between 

 8.0 P.M and 3.30 a.m., on fifteen occasions extending over six nights and over an area of 

 (roughly) 45 X 15 minutes. Similarly all the 55 * epiplanktonic specimens of imbricata 

 were captured between 8.0 p.m. and 3.30 a.m., on ten occasions extending over four nights 

 in an area of about 35x15 minutes. In such cases the question is not one of a confined 

 swarm, but of similar, if scattered, observations over a fairly large area and period. 



The following species showed increased numbers in the epiplankton by night : — curta f, 

 dai^lmoides, elegans, hycdophyllum, imbricata, mciffnaf, A larvae f, rotundata f, spinifera; 

 of these nine, three were never captured at or above 100 fathoms by day, one only once, 

 one only twice. The following showed no such variation in number by day and night : — 

 haddoni, loricata, procera, spinirostris, zetesios, globosa t, but in the last case the 

 plurimum. seemed to rise at night. 



A point wliich requires consideration is, how far the plurima observed during the 



"cruise may have been due to some specially favourable conditions on a particular night. 



On investigation this appears to have been partially the case ; this will be seen from the 



following list, in which are given, for the more plentiful species, those hauls at which 



the greatest average number per hour were captured : — 



It is obvious that the night on which hauls 32 m, n, o, p were made was exception- 

 ally rich : my log records " very fine, smooth, pitch-dark " ; but it is doubtful whether 

 the weather had any bearing on the point, as all these four hauls were made at 75 and 

 100 fathoms. This night, however, was not uniformly the best for all species : magna 

 was far more plentiful in 25 g and 34 d ; dajyhtioldes again was most plentiful on yet 



another night. 



* Actual numbers. 



t Compare figure L. 



