SOME RESULTS OF THE INTERNATIONAL FISHERY INVESTIGATIONS. 481 



a general scheme as the following : At the beginning of the year there 

 is little variety in the composition of the plankton, and it is relatively 

 scanty in amount. But towards March and April it becomes astonish- 

 ingly rich and abundant. Diatoms are present in great quantity, and 

 we have the eggs and larvae of the fishes which are then spawning. A 

 little later on the larvee of hosts of invertebrate animals appear, and 

 towards the summer these and the fish eggs and larvre begin to decrease. 

 About this time also the diatoms occur in least abundance. Cojlenter- 

 ates, medusie, siphonophores, medusoid forms of hydrozoa, and protozoa 

 such as Noctihica and Ccratium occur in great abundance. Then in the 

 autumn there is again a luxuriance of diatoms, these organisms attain- 

 ing their second yearly maximum of abundance, which, however, is 

 usually less than the spring maximum. As winter approaches, the 

 plankton again becomes less varied and abundant. 



Then we have " swarms " of organisms appearing in the plankton. 

 Over restricted areas of sea one kind of organism may be present 

 almost exclusively, and this swarm may drift over a large extent of sea. 

 Many such instances are recorded in the International publications. 

 Even if the usual varied plankton is found, we may be able to trace the 

 (passive) migration of certain characteristic constituents from place to 

 place. An excellent example of this is to be found in the distribution 

 of the jellyfish Muggiccn in the w^aters of the English Channel and Irish 

 Sea in 1904. The plankton observations made by the Marine Biological 

 Association in that year* show that a shoal of these animals coming up 

 from the Bay of Biscay reached the English Channel about April. 

 Dividing, one part of this shoal entered the Channel, and by the begin- 

 ning of September had travelled as far east as Portland, after which 

 month it gradually retreated to the west. The other part of the shoal 

 rounded Land's End, and by the end of September had gone as far north 

 as Cardigan Bay and South Arklow. About this time a southerly drift 

 of water from the Irish Sea had begun to divide the shoal, and part was 

 driven to the south and west coasts of Ireland. By the end of Novem- 

 ber the shoal had reached far up the west coast of Ireland, and was 

 observed in Galway Bay. 



Now the distribution of this shoal of animals depended on three 

 things : (1) the true drift of Atlantic water towards our shores, (2) the 

 superficial drift of the water duo to winds, and (3) the reproduction of 

 the animals. Probably the large hydrographic phenomena which we 

 have already considered had not much to do with the migration of the 

 shoal. l)Ut in another plankton study carried out by the International 

 vessels f we have a clearer instance of the conveyance of the plankton 



* See Goii,!:,'h, Pnhlirations ric Circonstance, No. 29, 1905. 



t See Dainas, " Notes biologiques sur les Copepodes de la mer iiorvegienne," Publications 

 de Circonstance. 



