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Part III. — Seventeenth Annual Bepori 



occurred, but very sparingly, from the surface down to ten fathoms. In 

 the gatherings collected in August and October 1898 its distribution was 

 somewhat similar. 



Daphnia galeata was more or less plentiful, except in the gatherings 

 collected during the winter months. Large specimens of the Daphnia 

 with strongly crested heads were obtained in Loch Oich ; a considerable 

 variation in the form of the head was also observed. 



Bosmina also exhibited a considerable amount of variation. 



Holopedium gibberum occurred very sparingly in Loch Oich. It was 

 not observed during the winter months. The seasonal changes appear to 

 affect very much the distribution of Holopedium. 



Camptocercus was observed in only one gathering, collected at five 

 fathoms on 6th October 1898. The post-abdomen of this Camptocercus 

 is more characteristic of C. rectirostris than of C. macrurus — -the species 

 to which British specimens have usually been ascribed. 



Alona affinis. A single specimen of this Cladoceran was obtained in a 

 gathering from ten fathoms. 



Polyphemus was apparently absent from the gatherings collected in 

 December and January, and this tends to confirm what has been said as 

 to its susceptibility to seasonal changes. 



Bythotrephes and Leptodora show a distribution very similar to the 

 distribution of the same species in Loch Ness. 



(3) Loch Lochy. 



The distance between the north-east end of Loch Lochy and the 

 south-west end of Loch Oich is slightly over one and a half miles, and 

 there is a difference of only a few feet between the levels of the two lochs. 

 From the frequent passage of vessels to and from the East and West 

 Coasts, a considerable quantity of water makes its way from Loch Oich 

 through the canal into Loch Lochy, and probably conveys some of the 

 Loch Oich Entomostraca into the neighbouring loch, and thus gradually 

 tends to bring about a more or less marked uniformity in their pelagic 

 faunas. Littoral species — that is, species whose habitat is about the roots 

 or amongst the foliage of the aquatic vegetation of the shore and shallows 

 of lochs — are less likely to be affected by these movements of the water 

 than those are that live in the open ; and therefore a greater dissimilarity 

 may exist between the shore and bottom faunas than between the free- 

 swimming species of lochs which are so situated that the overflow water 

 from the one passes into the other. The study of the dispersion of 

 species is of wide interest and has an important bearing on the question 

 of what are, or should be, considered distinct species or varieties. 



Temperature Observations. 



So far as the records are comparable, the temperature of Loch Lochy 

 shows rather less seasonal variation than Loch Oich, which is no doubt 

 owing to the greater body of water in Loch Lochy. 



The annexed Table contains a number of temperature observations 

 taken in this loch : — 



[Table. 



