236 FOUNDERS OF OCEANOGRAPHY 



to a good deal of the phosphorescence of the sea. It may 

 occur in dense swarms, especially in inshore waters, and may 

 be abundant in one place and totally absent in other localities 

 not far distant. It has been found swarming in the sea 

 round Anglesey in August, while none were found round the 

 Isle of Man. A few years ago it occurred in enormous 

 abundance in the Barrow Channel in December, which is 

 unusually late for these coasts ; but in the Baltic it usually 

 appears in great swarms late in the year. Its home, where it 

 is commonly present throughout the year, is said to 

 be the English Channel and the southern part of the North 

 Sea (see also p. 214). 



The Diatoms and the Dinoflagellata and their allies are 

 frequently grouped together as " Phytoplankton " in opposi- 

 tion to the animals (Zooplankton) which follow : — 



The Copepoda, small shrimp-like Crustacea averaging 

 about an eighth of an inch in length, are the most important 

 group of the zoo-plankton and are found in all seas at various 

 depths and at almost all times of year. Some, such as the gen- 

 era Parapontella and Temora (Plate XXIII), are characteristic 

 of coastal waters (" neritic "), while others, such as Acartia 

 (Plate XIX, Fig. 4) and Anomalocera, are " oceanici" in origin. 

 Calanus finmarchicus (Plate XIX, Fig. 3) is one of the largest 

 of Copepoda found in the British seas, and probably the most 

 important from a practical fisheries' point of view, as it is an 

 element in the food of various migratory fishes such as the 

 mackerel and the herring. Its home appears to be in the 

 North Atlantic to the south of Iceland, but it occurs on 

 occasions in large swarms in various other parts of the 

 European seas, and appears to be a constant inhabitant of 

 deep water near the bottom of some of the Scottish sea- 

 lochs. 



Sagitta (Plate XX, Fig. 2), the "arrow- worm," and Tomop- 

 teris are both transparent, pelagic worms frequently met 

 with in the plankton and usually more abundant in deeper 

 zones of water than at the surface. 



