BIOLOGY OF THE SCOTTISH LOCHS 277 
agrees with the plankton of the rest of Europe, and the world 
generally, then the special peculiarities which distinguish it. Before 
doing so it will be necessary to examine the composition of the 
plankton. The number of organisms which have been taken in 
the plankton-collections, i.e. in the open water of the lochs, is very 
considerable. On a scrutiny of the lists of species taken in the 
plankton-nets it is found that a large number of them must be ex- 
cluded as not truly belonging to the plankton. This results from 
the narrow form of most of the larger lakes, which makes it easy for 
littoral forms to be driven out to the open water during storms. 
The same effect is produced in broad but shallow lakes by the stirring 
up of the muds, by which bottom forms become mixed with the true 
plankton. The plankton is very often impure, but experience teaches 
what are the true plankton organisms, and, moreover, in the larger 
lakes very pure collections may be got after a period of calm weather. 
Excluding casuals, the plankton lists are not very extensive. 
The relative frequency of the species in the following lists is 
indicated by only three terms, general, heal, and very local. It is 
judged that more accurate discrimination is not at present possible. 
ZOOPLANKTON 
Crustacea. — Diaptomus gracilis, Sars. General. 
D. laciniatus, Lillje. Local. 
D. laticeps, Sars. Local. 
D. zvierzejshii, Richard. Local. 
, Cyclops strenuus, Fischer. General. 
Diaphanosoma hrachyurum, Lievin. General. 
Holopedium gibherum, Zaddack. General. 
Daphnia hyalina, Leydig. General. 
Bosmina ohtusirostris^ Sars. General. 
B. longirostris (Mull.). Local. 
B. coregoni, Baird. Very local. 
Polyphemus pediculus (Linne). General. 
Bythotrephes longimanus, Leydig. General. 
Leptodora kindtii (Focke). General. 
Rotifera. — Floscidaria pelagica, Rouss. ? Local. 
Conochihis volvox, Ehr. General. 
C. unicornis, Rouss. General. 
Asplanchna piiodonta, Gosse. General. 
Polyartlira platyptera, Ehr. General. 
P. euryptera, Wier. Local. 
Triarthra longiseta, Ehr. Local. 
