GON Y AUL AX . 



33 



anterior half of the shell breaks longitudinally, the contents come ont 

 from the shell, and gradually change to the spherical shape. If the 

 discolored water is kept without any preserving reagent, the water 

 emitts, after about a week, a pungent odor of hydrogen sulphide and 

 the shell of Gonyaulax swells which is finally dissolved. The proto- 

 plasmic contents which have come out of the shell retain the spherical 

 shape, with the chromatophores gathered in the centre. This fact is 

 interesting, as a sample of similarly discolored water which was observed 

 in September of the previous year (1891)) in the Bay of Toba and which 

 caused a great mortality among fishes, presented exactly the same ap- 

 pearance when it came to my hand from Mr. Mikimoto who had bottled 

 it ten days before without adding any preserving reagent. This makes 

 it highly probable that the cause of discoloration on that occasion was also 

 Gonyaulax pol y gramma. 



Besides this species of Peridurales, the discolored water contained 

 a species of Ceratium and Prorocentrum micans, Ceratium tripos, 

 Chaetoceras, and some nauplius larvae were also rarely found. In the 

 discolored water which I observed on the northern shore of Masaki 

 Island, Prorocentrum and Ceratium were very abundant At the same 

 time, in the ordinary clear water of the Bay, the plankton is rich in 

 Bacillariaceae (such as Bacteriastrum, Bhizosolenia, Chaetoceras) Cope- 

 poda, Noctiluca, Appendicularia, Sagitta, Nauplius and the lai'vae of 

 Polycbaeta and Gasteropoda. Thus, there was a great difference between 

 the living organisms of the discolored water and of the ordinary sea-water 

 close by. This difference seems to show that the discolored water 

 is unfitted for the existence of Copepoda, Noctiluca, Bacillariaceae &c. 

 while it seems specially suitable for the propagation of the unicellular 

 organism, Gonyaulax. The chemical properties of the discolored water 

 are probably different from those of the ordinary sea-water, but I have 

 been unable to make investigations on the matter. 



The occurrences in an excessive abundance of minute unicellular 

 organisms, as the cause of unusual coloration of sea-water have been 

 described before. Dr. Carter described Peridinium sanguineum as 



