19 



I Rhizosolenia styli- 



4, Styli-Plankton (symbol S). Typical forms { 



[ formis 



(Ceratium tripos, 



5. Tripos-Plankton Tp [ Rh ,'izosolenia alata f. 



[ gracillima 



Neritie Types 



1 . Southern Neritie I 



i VT \ m_ i / ^ Chcetoceros didt/mum 

 Plankton (symbol Nm). Typical forms ( 



f S/celetonema costa- 



tum, Leptocylin- 

 drus danicus 



i Chcetoceros furcella- 

 tum. Fragilaria 



\ oceaniea 



f Coscinodiscus concin- 



\ nus 



! Halosphosra viridis 



2. Northern Neritie 

 Plankton Ns 



3. Arctic Neritie 



Plankton Ng 



4. Concinnus Plank- 

 ton Nc 



5. Halosphsera 



Plankton . Nh 



We will first refer to tbe Oceanic Types. 



As we have already stated, the conditions in the open sea are 

 similar throughout great stretches of ocean, and it commonly hap- 

 pens that one species predominates to such an extent as to deter- 

 mine the nature of the Plankton. Therefore such a classification 

 as that made out by CLEVE is practical and applicable in many 

 instances, even if one differs from him in the hypotheses attached 

 to it. 



Before proceeding further, we would remark that CLEVE'S type, 

 Sira-Plankton, includes Oceanic (Coscinodiscus) and Neritie (Tha- 

 lussinaira) forms. For the oceanic, one ought therefore to establish 

 a new type. Disco-Plankton, and place Sira-Plankton amongst 

 the Neritie forms. 



With this change, CLEVE'S 5 types naturally embrace the 5 

 Pelagic Diatoms which, also, from our observations, most generally 

 occur as prevalent species in the Plankton. 



We thus get: 



1. Disco-Plankton 



2. Tricho- Plankton 



3. Chseto-Plankton 



4. Styli-Plankton 



5. Tripos-Plankton 



Coscinodiscus oculus iridis 

 Tfialassiothrix longissima 

 Chcetoceros deeipiens 

 Rhizosolenia stylifarmis 

 Rhizosolenia alata 



A deciding question as to the correctness of CLEVE'S hypo- 

 thesis concerning the movements of the Plankton may be put, viz., 

 whether a type of Plankton - - or Plankton community if we may 

 MM; a term employed for the fixed plants cannot become spread 

 in other ways than by means of the ocean currents. If CLEVE'S 

 theory were right, it surely ought to be proved that the Diatomic 

 communities cannot spring up to any great extent in parts remote 

 each other, even if the natural conditions were similar. In such 

 a case one might, justifiably talk, lor instance, of Cha:to-water and 

 Tricho-water, in which the organisms could be regarded in the 

 same light as leading fossils in geological strata. 



The Swedish scientists have not endeavoured to being forward 

 any proof, of this being so, and, in reality, such could not be done. 

 On the contrary, CLEVE'S own tables shew us the possibility of such 

 independent development. 



If but quite small numbers, for instance of Chseto, Disco and 

 Tricho Plankton species could be found amongst an abundant Styli- 

 Plankton, the possibility is raised of the other species becoming 

 gradually developed at the expense of the Styli-Plankton when 

 the waters coo] or possibly undergo other, but hitherto unknown 

 hydrographical changes. The opposite would occur by an increase 

 of warmth, and even in the Polar current itself a Styli-Plankton 

 might gradually become developed provided it contained some in- 

 dividuals of Rhizosolcnia styliformis which had survived the cold, 

 or which might enter it from adjacent currents. 



If we regard CLEVE'S Table I [97] in which he has placed a 

 number of, in his opinion, typical samples of Styli-Plankton 

 from the most different portions of the Atlantic, we will perceive 

 that in the 12 samples the following were met with. 



Styli-Species 

 Chaeto- 



Tricho- - 

 Tripos- 



Rhizosolenia styliformis . was found in 10 samples 



( Chcetoceros boreale - 4 



| deeipiens . . . . - ti 



I Thalassiothrix longisaima ,. - 5 



\ Rhizosolenia semispina . . - 3 



Rhizosolenia gracillima . ,. - 4 



In Table II, 7 Types of Chseto-Plankton 



was found in 7 samples 



( Chcetcceros boreale 



Chaito-Species 



I decipiens . . . 



Disco- 

 Tricho- - 



Styli- 

 Tripos- - 



Coscinodiscus oculus 

 i Thalassiothrix longissima . 

 \ Rhiz )solcnia semispina . . . . 



xtt/liformis . . 

 gracillima . . 



7 

 1 

 5 

 4 

 5 

 4 



Of Tricho-Plankton, p. 6, 10 Typical samples 



{Thalassiothrix longissima . . was found in 6 samples 



Disco- 



Chteto- - 

 Styli- 



Rhizosolenia semispina . . . 



Coscinodiscus oculus iridis , 



( Chcetoceros boreale 



| decipiens , 



Rhizosolenia stylifarmis . . 



6 



a 



3 



2 

 3 



It will be seen that even in these samples which CLEVE him- 

 self has chosen, there are sufficient of the other Plankton Com- 

 munities to allow of their becoming developed when a change in 

 the conditions of existence occurred. 



In nature, the communities are, in most instances, even still 

 more mixed, even when one predominates. If one refers to our 

 PI. 4, Fig. 1, it will be seen that at Station V, the Chseto-Plank- 

 ton predominates, with Tricho- and Disco-Plankton in a subordinate 

 degree. At Station VI, the same exists. At Station VII the three 

 Oceanic types are equally developed. At Station VIII, the Disco- 

 and Tricho-Plankton predominates, with Chseto- and Styli-Plankton 

 to a subordinate extent. 



