THE ROTIFERA OF THE SCOTTISH LOCHS. 185 
Note on tHe Rotirera or PonDs, AS COMPARED WITH [AKEs. 
Neither physically nor biologically can any hard and fast line be drawn between 
lochs and ponds. In making the bathymetrical survey, the practice was to examine 
any body of water on which a boat was found, or could easily be placed, omitting as a 
rule those of less than quarter of a mile in greatest diameter. 
Some lochans of less than quarter of a mile in length—for example, Lochan Dubh at 
Lochailort—were of such depth that the temperature and the biological phenomena 
showed a correspondence with our greatest lakes, rather than with shallow lakes or 
ponds. On the other hand, some very considerable lochs were so shallow that the tem- 
perature had the extreme range found in small ponds, and the biology corresponded. 
The foregoing list of Rotifers is restricted to species found in lochs which were 
bathymetrically surveyed. When practicable, we also examined ponds adjoining the lochs 
for purposes of comparison, and periodical collections are being made from certain small 
ponds, in order to compare the annual cycle of changes with that which occurs in lochs. 
This investigation is still incomplete, and will be dealt with when finished. A full 
account of the Rotifera of ponds would be too extensive to be included here. At present 
it is only intended to contrast the relative frequency of the species in our list in lakes 
and ponds, and to describe a free-swimming Bdelloid which came to light in the course 
of these researches. . 
All the Rhizota in the list, except the species of Conochilus, Floscularia pelagica, 
and F. mutabilis, are commoner in ponds, and are not very commonly found in lakes. 
Even the powerful swimmer, Pseudcistes rotifer, prefers ponds and ditches. Of the 
Bdelloida, the various genera are different in their habits. On the whole, the oviparous 
kinds are more at home in lakes, the viviparous in ponds, but there are exceptions. Most 
of the species of Philodina which we have recorded are very much at home in lakes, 
and several of them, with the related Microdina, are the most characteristic of lake- 
margin forms. P. citrina, P. acuticornis, and the two viviparous species are pond- 
dwellers. 
The genus Fotifer is on the whole rare in lochs. I have found no species common 
in lochs except the parasitic FR. socialis; R. macroceros is next in frequency, the 
others rare. 
In ponds adjoining Loch Ness we found R. vulgaris, R. citrinus, R. tardus, 
R. longirostris, R. macrurus (which is not in our list as a lake species) all common 
and abundant. A. neptunius is frequent, and FR. trisecatus not very rare in ponds. 
R. macrurus is most at home im bog-pools, and R. longirostris among dirty moss. 
Many of the Callidine are ubiquitous—equally at home in ponds, lochs, and else- 
where. None are particularly characteristic of lake-margins, but C. muricata, 
C. erucicornis. and C. incrassata (not yet found in lochs) are true pond species. 
The pellet-making Callidinx, though well represented in our list, are with few 
exceptions properly peat-bog species. C. elegans (?), C. pusilla, and C. longiceps are 
