THE ROTIFERA OF THE SCOTTISH LOCHS. 155 
for a definite time through the open water of the lake, as far as convenient from the 
shore. It is advisable to draw them for a time at some distance below the surface, say 
20 feet, as well as at the surface, because in extremes of weather the animals sometimes 
retire from the layer close to the surface. They should be examined as soon as possible 
after collecting, as most of them very quickly die under the changed conditions. While 
some will survive for a time in the bottles, others, such as Notholca longispina, are so 
sensitive to change of temperature that they are seldom found alive when the collections 
are brought home. 
Although very many Rotifera are free-swimming, comparatively few are limnetic, 
albeit, if the whole world is taken into account, the number is considerable. By 
limnetie Rotifers is meant such species as normally take up their position, far from the 
shelter of plants, in the open water of the lake, and extend to every part of it. 
Of the truly limnetic Rotifera, few occur together in any one lake; their range may 
be world-wide, but their distribution is local. A species regarded as limnetic in one 
part of the world may be only known as an inhabitant of the lake-margins elsewhere. 
It is well to distinguish, among the limnetic species of one lake or district, between 
these more or less local species, and the others which belong to that universal 
association of limnetic animals which are present in all lakes offering normal conditions. 
Dr Lunn, in the paper above cited (34), gives a short list of species which he 
characterises as ‘‘ the cosmopolitan stock of plankton Rotifers.” These are Polyarthra 
platyptera, Synchxta sp., Asplanchna priodonta, Anurxa cochlearis, Anurea 
aculeata, Notholea longispina, Conochilus unicornis, and Triarthra longiseta. 
On the whole, Dr Lunn’s list embodies the species which we find to be most 
generally distributed in the Scottish lochs. Inasmuch, however, as it is dificult to 
avoid generalising from partial data, it may be useful if we examine Dr Lunp’s list in 
the light of our experience in the Scottish lochs, and indicate some points to which we 
must take exception. 
Scotland is pre-eminently a country of lakes. Considering its situation in a 
temperate region, the great number of its lakes, many of which, though not of great 
extent, are from their depth to be classed among great lakes, we would be justified in 
regarding Scotland as favourable for the existence of the cosmopolitan stock of Rotifers. 
We would expect to find this stock in all our greater lakes; we would at the least 
expect that no member of it would be absent or rare. The fact that five out of 
Dr Lunp’s eight cosmopolitan species are our commonest limnetic species shows that 
Scotland is suitable for them. These five most thoroughly limnetic species are 
Polyarthra platyptera, Asplanchna priodonta, Anureu  cochlearis, Notholca 
longispina, and Conochilus wrcornis. 
Let us now consider the three species which do not live up to their cosmopolitan 
character in Scotland. 
Syncheta sp. is unsatisfactory, as Dr Lunp does not name the species which he 
regards as cosmopolitan. Various species of Synchezta, especially S. pectinuta and 
