1898.] PLANKTON OF THE FAEROE CHANNEL. 581 



in the Faeroe Channel is very perplexing. On the second and last 

 days out of eight in 1896, they were at or near the surface in enor- 

 mous quantities (96 to 140 specimens in a haul of 10 to 15 

 minutes) ; on the other six days, they were not only scarce or 

 absent at the surface, but could not be found even by the deep- 

 water net. Our position was altered several times between the two 

 days of their swarming. This seems to imply that D. tritonis 

 occurs in patches, with a few outliers in between the patches. 

 Similar swarms of this species were observed in the Faeroe Channel 

 by the ' Triton ' in 1882 l , by the 'Holsatia' in 1885, by the 'National' 

 in 1889. 



Brandt 2 , in an interesting discussion of swarms such as these, 

 seems to incline to the view that they are produced by wind and 

 current action ; but it is a little difficult to imagine how the effect 

 of these agents would gather scattered organisms into a broad swarm 

 in the open sea, except in an eddy or backwater ; although they 

 might make "wind-rows " in the open sea, or swarms in a closed 

 area such as the Mediterranean. Further, if wind and current- 

 were the main direct agents in collecting swarms of D. tritonis, 

 other organisms of the same powers of locomotion ought also to 

 swarm at the same time ; this is not my experience, nor, so far as 

 1 know, have other observers recorded this as a feature of the case. 



I should prefer for the present to regard a swarm of D. tritonis 

 mainly as the result of a period of great reproductive activity. In 

 the case of an organism with a rapid power of multiplication and 

 definite reproductive periods (whether due to food, temperature, or 

 other causes), a very large number of individuals will soon be pro- 

 duced nearly simultaneously ; if they have but little power of self- 

 locomotion, as long as they lie in the track of fairly uniform wind 

 and current, such as the North Atlantic Drift ("Gulf Stream"), 

 there seems to be no reason why they should be parted one from another. 

 In an eddy, such as the Sargasso Sea, where there are no con- 

 stant winds or constant currents, the tendency will probably be 

 for every little shift of wind to part them. The swarms of various 

 organisms met by the ' National ' were apparently all in the track 

 of great ocean-currents, and were conspicuously absent from the 

 Sargasso Sea. 



If my suggestion is correct, then in still or steadily moving 

 water a few Uoliolum " Ammen," fairly close together, will produce 

 a crop of " Pflegethiere " by asexual generation more numerous 

 than themselves ; and although we do not know the rate of 

 reproduction of the "Amme" in throwing off "Pflegethiere," 

 still that each "Pflegethier" may throw off an enormous number 

 of sexual forms is obvious from the hundreds of buds on the 

 stolon of each Pflegethier. The rate of reproduction is extremely 

 rapid ; and I see no reason to believe that in a constant current 

 the family would not move forwards as a whole. 



1 " .At times the Doliolum appeared to be in vast banks, where they were very 

 numerous ; between these banks there were always a few stragglers." (Murray 

 in Herdman, op. cit. p. 112.) 



- Brandt : in Eeisebeschreibung der Plankton Expedition, p. 356 (1892). 



PROC. ZOOL. Soc. 1898, No. XXXIX. 39 



