CANADJAX I'lSUERIES EXI'EI>[T1()\ . lUI',!-', 493 



The species which in June predominate in the surface layers are, on the one hand, 

 the brown Cilioflagellates Dinophysis norvegica and D. acuminata (Especially at 

 stations 5, 6, and 8) ; and, on the other hand, infusoria. Foremost among these we 

 find the remarkable Mesodinixim ruhrum, and species of the genus Lahoea, the distri- 

 bution of which is, up to the present, but little known, as all previously known methods 

 of collection and preservation render them unrecognizable. Of the Lahoea species, 

 two in particular are found to predominate, viz., L. conica Lohmann, and L. vestita 

 Leegaard. Both the Mesodinium and these two Lahoea species are distinguished by 

 the presence of chlorophyll (covered by a brown colouring matter) and thus belong to 

 the producers of the plankton. Mesodinium is, according to Lohmann's investiga- 

 tions, doubtless colourless in itself, but lives symbiotically with small brown algae, 

 which fill the whole of its cell. The two Lahoea species — in contrast to several others 

 of the same genus — are brown, which fact I have been able to convince myself of by 

 investigation of living material; up to the present, however, I have not been able to 

 ascertain exactly whether the colour is due to captured algal cells or belongs to organs 

 in the cells of the infusoria themselves. In any case, these three species appear to have 

 been the most important C'02-assimilating organisms in the gulf of St. Lawrence in 

 June, 1916. Lahoea conica has hardly been found before at any place in such great 

 quantities as here (over 3,000 per liter at stations 6 and 8, over 5,000 at station 16). 



It may appear remarkable that just these interesting organisms which unite the 

 nutritive power of the plants with the lively movement of the animals, should be the 

 first to populate the surface layers after the conclusion of the diatoms' period of 

 development, but as their development otherwise is at present little known, we cannot 

 deeidte whether the feature in question is characteristic of the gulf of St. Lawrence. 



A further noteworthy point is the comparatively large quantities of colourless 

 Gymnodinium species, especially G. Lohmanni. This Cilioflagellate subsists by absorb- 

 ing solid bodies into its interior; whether it is also capable of absorbing dissolved 

 organic matter from its surroundings has not yet been determined. An occurrance of 

 3,000 per liter (station 8) or 5 per ec. is a very considerable quantity for so large an 

 organism, obliged to live upon organic food, and may be taken as a certain sign that 

 it finds particularly favourable conditions for development. 



Cruisk of the "Acadia'' May 29 to 31, 1915 (Table 2). 



The samples from the Princess are supplemented in an interesting manner by the 

 series taken somewhat more than a week earlier by the Acadia in the sea outside the 

 Gulf of St. Lawrence. Most of the stations have, however, a plankton surprisingly 

 poor in quantitative respects; this applies especially to stations 2, 4, 10, and 12. The 

 quantities found are in reality so small that we must presume that the conditions for 

 development cannot have been favourable to the phytoplankton. Of producers, only 

 quite small quantities were found of colourless Cilioflagellates (Gymnodinium Loh- 

 manni), with infusoria (Lahoea sipecies) somewhat more numerous. The method of 

 preservation leaves it an open question whether Coccolithophoridae, whose calcareous 

 shells would have been dissolved by the acid employed, or small flagellates, which are 

 difficult to find in a preserved state, were or were not present. If no such sources of 

 nutrition occur it will be difiicult to explain the finding of so rich a stock of organisms 

 unable to assimilate carbonic acid for themselves. At station 10, however, we find at 

 the surface a quite rich stock of the assimilating Lahoea conica. 



An exception is formed by the two stations 6 and S, which have a rich diatom 

 plankton, with Leptocylindrus danicus, and at station 8 also Chcetoceras' dehile. This 

 plankton resembles both in quantity and quality that Avhich may be found on the 

 coasts of Northern Europe in May. Both the composition in regard to species, and 

 the abundance, point to a distinct coastal influence; the species are neritic, and the 

 rich development is most probably due to dissolved nutritive matter from the coastal 



