THE PLANETOID OF EASTERN IS OVA SCOTIA WATERS 



3 



SESSIONAL PAPER No. 15a 



protoplasm, the so-called ' Flagellata,' do not exceed %ooo of an inch in diameter, and 

 slip through such a mesh with ease, unless accidentally arrested by the threads. 



As to the one-celled animals which, of course, feed on these smaller plants, they 

 belong to the various groups represented on Plate IV., and some of them form with 

 Peridinia and Diatoms, a conspicuous part of the food of oysters and similar molluscs. 



Again, the plankton contains many young phases of higher animals which swim 

 about for the earlier part of their life and afterwards settle down to more or less 

 sedentary habits. Such is the case with the sea-urchins, worms, molluscs, &c., some of 

 the young of which are represented on Plate V. These larvae are, of course, dependent 

 on the minute life of the plankton for their food, and are themselves devoured by 

 larger animals. 



But there are also adult animals of small size rarely more than the | of an inch 

 or so in length, which are constantly eating up the crop of microscopic plants, and 

 which themselves form the bulk of the food of plankton-feeding fish; such are th^ 

 .Copepods represented on Plates VI., and the Tunicates, on Plate VII. And, finally, 

 reference should be made to the floating eggs of various fishes like the cod, occurring 

 in enormous numbers, few of which ever reach maturity, but are destined to furnish 

 nourishment to the plankton feeders. 



Many of the creatures and eggs referred to are exquisitely adapted to their floating 

 (pelagic) life, by their extreme translucency, which makes them almost invisible in 

 the water. Such is notably the case with forms like those shown in Plate V., Fig. 13, 

 and Plate VII., Figs. 11 to 13. 



The following account of the organisms observed at Canso is intended as a pre- 

 liminary one, one of the results of which it is hoped may be the lightening of the 

 initial labours of future investigators into the Canadian plankton, and another, that 

 some workers may thereby be induced to enter this interesting fleld of research, which 

 requires, owing to the vast extent of our Dominion waters, to be sub-divided to give 

 entirely satisfactory conclusions. 



PERIDINIALES. 



PROROCENTRIDJE. 



This family embraces the simplest forms of Dinoflagellata, and one of the genera 

 at least suggests by the symmetry of its bivalve shell a relationship to the Diatoms, 

 the colouring of which they also share. The characteristic girdling furrow of the more 

 typical members of the order is absent. 



EXUViAELLA. — CienJcowsky. 



This differs from Prorocentrum in the lack of the prominent anterior spine of 

 that genus. The specimens observed at Canso, and more frequently at Malpeque, 

 P.E.I., belong to the species E. marina (Plate I., fig. 1), but there appears to be a 

 slight difference in that the posterior half of the shell is decorated with some short 

 projecting spines which may entitle it to the varietal name 'hispida/ The dimen- 

 sions are 42 x 33/x. 



PROROCENTRU M . — Ehrh . 



P. micans E. (Plate I., fig. 2) also more abundant at Malpeque, appears to be 

 identical with the common European form; it is longer and slenderer than Exuviaella 

 and less symmetrical in outline. The two foregoing species, especially the latter, are 

 important constituents of the oyster's food. 



