Density of Flagellates and Myxophyceae 221 



from those of otlier regions. Table 2 gives several examples of 

 such facts. 



Of course, Table 2 is pro\'isional and has only a seasonal 

 value: off Algeria and Lybia only results for June and July are 

 knov^n. However, several facts seem obvious and interesting: 



The percentage of calcareous flagellates is greater than 30 

 per cent throughout the Mediterranean (Adiiatic excepted) and 

 in the central Indian Ocean. It is lower in the Strait of Gibraltar 

 and in the Atlantic, owing to the large local numbers of naked 

 flagellates and Peridinians. 



Nostoc is very sensitive to mud in suspension, and perennial 

 only when water is very pure, as off Monaco and in the central 

 Indian Ocean. The same fact was discovered by Hentschel (7) 

 for "olivgriinzellen" (Microcystis) in the deep southern Atlantic. 



EXAMPLES OF STATIONS RICHER IN THE 

 APHOTIC ZONE (Fig. 1) 



Among the 281 stations examined by us, we have chosen 

 (Fig. 1) eight of the most remarkable places where the eu- 

 photic zone is, more or less, poorer in cells/ml than the deep sea. 

 Sometimes (see stations 6, 16, and off Tenes and Cherchell, 

 Algeria ) a considerable abundance of pahnelloid Cyclococcolithiis 

 occurs only in aphotic layers. 



Nevertheless, one must maintain that, taking a mean value 

 of all stations, the deep zone is never extremely poor. It contains 

 generally one-fourth to two-thirds of the density of cells observed 

 in euphotic layers. For Cyclococcolithiis, Gymnodinians and 

 naked flagellates, the commonest relation is about one-half of 

 the surface value between 200 and 400 m, about one-third below. 



The scheme in Figure 1 represents only actual fertility 

 (cells/ml) for Cyclococcolithus (black lines) and naked flagel- 

 lates (dotted Hues). For the other kinds of cells, forming gen- 



Fig. 1. Density per ml of palmelloid cells of Cyclococcolithus (black 

 drawings) and small naked flagellates (dotted lines) in eight stations of 

 Mediterranean and of Indian Ocean. Those stations are chosen for their 

 deep richness. The density of Cyclococcolithus, off Cherchell (W. Algeria), 

 at 400 m depth, is today the world maximum of deep fertility (4,200 cells 

 ml. See text for other comments. 



