MARINE BIOLOGICAL STATION AT PORT ERIN. 79 



calculated that the Sardine takes as a meal about 

 20,000,000 of the small Ceratium tripos shown in fig. I. 

 at 2; while Professor Hensen has found 130 millions of 

 them in 10 cubic metres of water from the Baltic. This 

 and other kinds of Ceratium (1 and 3) are one of the chief 

 causes of the luminosity or " phosphorescence " of the sea. 

 Another little Protozoon which frequently causes the sea 

 to sparkle with light in the night is Noctiluca miliaris (fig. 

 I., 5), which is occasionally present in great abundance in 

 the Irish Sea. These all swim on the surface of the sea, 

 but there are many other Protozoa which have relatively 

 heavy though minute shells, and are usually found on the 

 bottom or attached to other objects. A good example of 

 this is Rotalia beccarii seen at 4, and belonging to the 

 Foraminifera. In some parts of the world Foraminifera 

 are so abundant that their minute living shells accumulate 

 as enormous deposits covering many million square miles 

 of the floor of the ocean, and those that existed in former 

 times now build up mountain ranges in some .parts of the 

 world. There are other Protozoa occasionally seen at the 

 seaside, such as Folliculina ampulla (No. 6), enclosed in a 

 delicate green-coloured shell and protruding its soft body, 

 bearing a fringe of numerous delicate hair-like filaments, 

 by the lashing of which food particles are wafted to the 

 mouth; and Tintinnus campanula (No. 7), a somewhat 

 similar form, enclosed in a conical shell, which floats in 

 the sea and can be captured sometimes by towing a fine 

 muslin net through the water. 



There is a group of microscopic plants, the Diatoms, 

 which is worthy of attention because of its great import- 

 ance as the food of many animals. Diatoms are 

 unicellular Algae, and a few of the commoner forms are 

 shown in the figure : 8 is a Biddulphia, 9 a Coscino discus, 

 10 is Chaetoceras secundum, and 11 Bacteriastrum varians. 



