624 



NA TURE 



[October 27, 189: 



one man to advance our knowledge on this line. Ever since 

 1854, when, as he tells us, he accompanied the great Johannes 

 Miiller to Heligoland and was there introduced by his master 

 to the marine wonderland, he has almost continuously pursued 

 the study of the Plankton. He believes that aquatic life in its 

 broadest features shows conditions of distribution similar to 

 those of terrestrial life, and that we may for the former as well 

 as for the latter distinguish five great geographical provinces, 

 each represented by characteristic forms of animals and plants, 

 (i) the Arctic Ocean; (2) the Atlantic; (3) the Indian; (4) 

 the Pacific ; (5) the Antarctic. 



All aquatic organic forms fall into two great divisions. (l) 

 Those which live free in the water, either swimming actively or 

 passively floating at the mercy of currents and winds. These 

 compose the Plankton. The Plankton thus includes the widest 

 ran :;e of organic size and form, from the minutest microscopic 

 organisms to the gigantic cetaceans. (2) Those forms which 1 

 live upon the sea bottom, either fixed or creeping about. To 

 these the term Benthos {t6 ^evOos, the bottom of the ocean) is 

 applied. The variety of forms living near the shore is known 

 to vary with the depth, while the forms characteristic of the 

 comparatively sliallow waters of the coasts are widely different 

 from those which inhabit the b )ttom of the deep sea. 



The number and the kind of forms composing the Plankton 

 are found to differ with the quality of the water, i.e. fresh or 

 salt. In the ocean there is a marked difference which is con- 

 ditioned by the distance from the shores, either of continents or 

 islands. There are many species of animals, particularly 

 certain coelenterates, echinoderms, and worms, which pass only 

 part of their life as fres-swimming animals ; for the remainder, 

 they are bottom dwellers. Such species are not usually found 

 far from the coast, and hence the true oceanic Plankton is made 

 up of forms which pass their entire life as free-swimming 

 organisms. By the presence or absence of these bottom-dwell- 

 ing species the Planktologist can determine approximately the 

 region where the forms were captured. 



A mere li<t of the genera, not to mention the species, of 

 plants and animals up to the present found to take part in the 

 constitution of the Plankton would be very formidable. The 

 range in size is enormous ; from the exceedingly minute uni- 

 cellular algce iTfi'rjjiT of an inch in diameter to the huge bulk of 

 many fishes and cetaceans. The microscopic forms constitute 

 the fundamental food supply in the cycle of marine life. They 

 are capable of exceedingly rapid multiplication, and furnish 

 nourishment for the myriads of large animals, which in time arc 

 preyed upon by the still higher forms. The inconceivable 

 number of individuals of the smaller species is demonstrated by 

 Prof. Hensen's determination of the number of individuals in 

 about two cubic yards of Baliic Sea water. This was found to 

 contain 5,700,000 distinct organisms; of these only about 

 150,000 were visible to the unaided eye. But very often 

 microscopic forms become so numerous as to form a slime upon 

 the surface of the water for a considerable area. Ships fre- 

 quently sail for miles through water coloured by these micro- 

 scopic organisms, e.g., the so-called "black water" of the 

 Arctic and Antarctic Seas, is a slime of diatoms, which serve 

 as food for the shoals of minute Crustacea and mollusca 

 (Pteropods, sea butterflies, and Cephalopods, squid, cuttlefish) 

 upon which the walrus and whales feed. In the warm regions 

 the inconceivably enormous quantity of diatoms are replaced 

 by another kind of alga;, the Ocillatorige, which often for an 

 area many miles in extent colour the sea a dark red or yellowish 

 brown. The Red Sea received its name from the abundance of 

 one of these algae, Trichodesmium erythrcBuin, which, according 

 to Ehrenberg, coloured the water along the shore a blood-red. 

 In the warm region also are found the huge floating banks of 

 Sargassum, or gulfweed, forming the so-called Sargasso Seas of 

 thi Atlantic and Pacific Oceans. These areas are found to have 

 a marine fauna and flora peculiar to themselves, but approxi- 

 mating in character to that of the coast waters. 



The simplest forms of animal life of the Plankton belong to 

 the groups of Infusoria and Rhizopods ; to the latter belong 

 those minute animals, the Foraminifera and Radiolarians, which 

 occur in such enormous quantities that their calcareous and 

 siliceous shells form the "deep sea ooze" which carpets the 

 bottom of the deep sea. It is the shells of these animals, too, 

 which have built the vast chalk beds in various parts of the 

 world. Among the multicellular animals which take a pro- 

 minent part in this marine world are many species of medusae 



NO. 1200, VOL. 4.6] 



(jelly fish) and the closely related Siphonophores, of which 1 

 beautiful Portuguese man-o'-war is the most familiar represcii 

 tative. The class of worms is represented by many ficc 

 swimming species ; but in the number of individuals it is far 

 surpassed by the molluscs, chiefly represented by the squids. 

 the pearly and paper nautilus, and the huge cuttlefish, and liy 

 the minute and delicately beautiful sea butterflies (Pteropods), 

 which occur in vast schools in the polar seas. Often, too, in 

 very considerable number are found the free-swimn-.ing larva' of 

 Echinoderms, as also many worm larvae, which, like the former, 

 pass their adult life upon the bottom. Every haul of the gau/( 

 net is certain to contain some representatives, of the great clas 

 of Crustacea, often great numbers of species, as well as uf 

 individuals. In distribution these seem to be subject to pretty 

 definite laws, and a careful study of the phenomena would be 

 of great interest. There are found also certain Tunicates, a 

 group interesting because many investigators believe that here 

 we find the transition from the invertebrate ancestor to the 

 higher plane of life of which man is at present the highest 

 representative. 



The vertebrates of the Plankton embrace the great group of 

 fishes, and in addition the marine birds, the seals and walrus, 

 and finally the cetaceans. In this connection, too, the enor- 

 mous number of fish eggs floating at the surface of the ocean, 

 as well as the transparent, newly-hatched fry must be mentioned. 

 Prof. Hansen hopes to get an idea of the approximate number 

 of fish of a given species in a certain area, computing the number 

 of eggs and fry of that species within that area. 



The phenomenon of marine phosphorescence is very widely 

 known with admiration and wonder. Its cause is chiefly or 

 solely bound up with organic life. The majority of pelagic 

 animals display the phosphorescent light in diff^erent degrees. 

 In some the entire living animal is brightly luminous ; in other 

 the light is limited to special organs. But much of the 

 phosphorescence of the ocean appears to be caused by the frag- 

 ments of dead organisms, and is connected with the presence of 

 bacteria. 



Since many chlorophyll-bearing organisms are found at depths 

 unpenetrated by sunlight, it has been suggested that the light 

 necessary for their growth is furnished by the phosphorescent 

 organisms. 



The composition of the Plankton is exceedingly irregular, 

 both in qualitative and in quantitative relations ; its distribution 

 in the ocean is also very irregular, both in time and in place. 

 The variations occur near the shore as well as far out at sea. 

 Very often the greater part of the mass of Plankton is made up 

 of organisms belonging to a single group. Sometimes unicellular 

 algas make up nearly the whole bulk, at another medusae, sipho- 

 nophores or ctenophores ; indeed, almost any group of marine 

 organisms may occur in such quantities as to compose more than 

 one-half of the total bulk of the Plankton, at that time and place. 

 The fundamental causes of variation in the quantity and quality 

 of the Plankton appears to be conditioned by time, climate, 

 and currents. 



Temporal Differences. — For a satisfactory determination of 

 these more complete observations are needed. Reliable data 

 can be furnished by the observations at the numerous marine 

 laboratories and zoological stations now springing up indifferent 

 parts of the world. The causes which underlie these yearly, 

 monthly, daily, and hourly variations are manifold ; in part 

 meteorological, in part biological. They are comparable to the 

 corresponding oscillations of the terrestrial fauna and flora, and 

 depend on the one side upon climatic and meteorological condi- 

 tions, and on the other upon the varying mode of life, particu- 

 larly upon conditions of reproduction and development. Just 

 as the annual development of most land plants is bound up with 

 a definite time of year, as the time of budding and leafing, of 

 blooming and fruiting, have in the "struggle for existence "be- 

 come adapted to the meteorological conditions, the time of year, 

 and other conditions of existence, so too the annual development 

 of most marine animals-is conditioned by definite habits, which 

 have become fixed by heredity. The yeariy variations may be 

 compared to the good and bad fruit years. This yearly varia 

 tion has been noted by many observers in case of many marine 

 animals. Our attention is often called to an example of it in 

 the unusual abundance or scarcity of the catch of certain food 

 fishes. 



Many marine animals, particularly certain medusae, siphono- 

 phores, ctenophores, molluscs, and tunicates, are found at the 



