THE FRESH -WATER LOCHS OF SCOTLAND. 433 



Synchata pectinata. Lochs Oich and Uanagan. 



Anopus testudo. Lochs Ness and Uanagan. 



Triarthra longiseta. In five lochs on the east side of the basin; 

 apparently a cold-water species. 



Gastropus stylifer. Loch Ness and five lochs to the east, and Loch 

 Aslaich to the west. 



Surcodina. ClathruUna was not seen except in the lochs of the 

 Great Glen. Sebela bicornis, West, though found in Loch Ness, was not 

 got in the plankton, but while dredging in the shallow water of 

 Inchnacardoch bay. 



Loch J'ess. Loch Ness was made the subject of a more thorough, 

 though still far from exhaustive, biological investigation than any other 

 Scottish loch. A very large proportion of all the lacustrine organisms 

 known in Scotland have been found in this loch. 



The great majority of the species in all the larger groups Crustacea, 

 Rot if era, Sarcodina have been got in Loch Ness, the only large group 

 not very fully represented being the desmids. Some of the small groups 

 have hardly been studied, except in Loch Ness, and it is the only loch 

 the abyssal fauna of which is fairly well known. 



To give any detailed account of the hundreds of species found in the 

 loch would traverse too much the same ground as the general report 

 on the Biology of the Scottish Lochs. There will therefore be given 

 here simply an epitome of the biology, and a comparison with the other 

 lochs in the Ness basin. 



The Plankton. The plankton is the average plankton of Scottish 

 lakes, with a very small admixture of the more local species. It is very 

 poor in species, and always very small in quantity. No approach to 

 " flowering " of the water has been noted. The greatest quantity was 

 collected in late autumn, 1903, during the night, when a considerable 

 migration from the deeper water to the surface evidently took place, 

 as the quantity collected during the preceding day was much less. The 

 plankton varies little throughout the year, a fact probably correlated 

 with the low annual range of temperature, which is less than 20 0- 

 Fahr., while the upper limit of about 60*0 is rarely touched. 



About half the species of Crustacea remain all the year round, 

 those which are absent in winter being Bythotrephes, Polyphemus, 

 Iseptodora, and Diaphanosoma. Holopedium was noted by Mr. Scour- 

 field, but was never found during the systematic investigation 

 afterwards. Diaptomus laticeps, Sars, appears to persist all the year 

 round, and was found carrying eggs in March, when the temperature 

 is at its lowest. ClathruUna was generally present, and Volvox 

 occasionally. 



There is a great contrast between Loch Ness and Loch Lochy in the 

 relative abundance of the phytoplankton. Loch Lochy is very rich, 



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