BIOLOGY OF THE SCOTTISH LOCHS 
297 
Crustacea. — Genus Diaptomus. — It is a curious fact that, although 
the three northern species of Diaptomus occur together in many 
districts, each is almost completely isolated, judging from the records 
available. There are rarely two of them in the same loch. There 
are over a hundred lochs in which one or other of these species is 
present, yet there are only nine lochs in which two or more of them 
were found, only two lochs in which all three were associated. 
In thirty-six lochs D. gracilis was found in company with one of 
the northern species, and in only two lochs (nan Cuinne and Baddan- 
loch, in Sutherland) were all four of the pelagic species present, A 
fifth British species, D. Castor^ has only been found in ponds, but 
Dr Scott has seen it in a few lochs. 
What are the conditions causing this isolation of species occupy- 
ing the same region ? Is it the physical or chemical properties of 
the water of the different lochs ? — all can live too;ether in some lochs. 
Is it climate — the different species will occupy adjacent lochs, among 
the same formations of rocks, and apparently identical surroundings. 
Is it altitude ? — D. lacmiatus, D. laticeps^ and D. gracilis range 
from almost sea-level to 2500 feet, at least. I), zmerzcjskii has a 
lower vertical range, and is more thoroughly isolated, occupying by 
itself extensive regions. The restriction in this case may well be 
climatic. 
A second species, too immature to be identified, was often found in 
lochs ; if mature individuals were found in their season, it might appear 
that there is more mixing of the species than is at present supposed. 
Diaptomus lackiiatus^ Lillje. — This species has been recorded by 
the Lake Survey in 37 lakes — 7 in Central and West Inverness ; 9 in 
Sutherland ; 6 in Ross (apart from Lewis); 13 in Lewis; 1 in the 
Clyde basin (Loch Lomond) ; and 1 in Ayrshire (Loch Doon). 
As it has a limited season, having been observed only during four 
months (from June to October), its range might be somewhat extended 
if all the lochs could be examined at the right season. As the records 
stand, they show an essentially Western and Highland species, the only 
locality in the south of Scotland being a truly dlpine lake. The most 
easterly records of the Lake Survey are in Sutherland, though Mr R. 
M. Clark found it a little farther east, in the western corner of 
Aberdeen, an alpine district. It ranges in altitude from lochs just 
above sea-level (Loch Shiel, etc.) to 2500 feet in Inverness. Consider- 
ing that it is most abundant in Lewis, it is curious that there are 
no records for Uist, nor for Orkney and Shetland. 
It is one of the species, according to Dr Wesen berg-Lund, 
belonging to Ekman's " boreo sub-glacial region, and outside of 
Scotland is known in Scandinavia, North Russia, and the alpine lakes 
of Switzerland, 
