BIOLOGY OF THE SCOTTISH LOCHS 
293 
to have seen the light before, give every sign that they can make good 
use of their eyes. They grovel down among the mud, apparently 
seeking shelter, and they prove, by the lively way in which they dodge 
the threatening pipette, that they possess good, serviceable eyes. 
Stylodiilus Gahretece^ — According to Martin, this species is 
general at depths of over 100 feet, and is sporadic in its occurrence in 
shallower water. In my experience both the abyssal Oligochaetes, of 
which Styloclrilus is one, are frequent at much less than 100 feet, 
but this is the nearest approach to a species limited to the abvssal 
region. 
Rhizopods. — It is among Rhizopods that the largest suggested 
abyssal element is found, and the evidence for it is sufficiently slender. 
Dr Penard, who has found so many abvssal Rhizopods in the Lake 
of Geneva, has been f^ood enouo:h to examine collections from 
Loch Ness. Admitting that the great majority of the species found 
belong to the habitual land fauna, especially to that of bogs, he claims 
that some half a dozen forms, ma'inhj varieties^ are such as he has 
found to be characteristic of deep lakes. Elsewhere I have given 
reasons for differing from Dr Penard's conclusions on this point.^ It 
seems to me unsafe, in dealing with the most plastic group of the 
Protozoa, to regard as peculiar species examples found in peculiar 
habitats, which only differ minutely in the form of external shells. 
Such forms might be produced by the peculiar conditions of the 
habitat on the individual during growth, and might not indicate 
established varieties at all. Be that as it may, Dr Penard agrees 
that the evidence is insufficient to warrant any definite conclusions. 
Physical Conditions in the Abyssal Region. — The most 
important physical conditions affecting the animals in the abyssal 
region of the lochs are, first ^ the uniform temperature, and second^ 
the absence of light. The pressure cannot be considered important 
to organisms filled with watery fluid of almost the same specific 
gravity as water ; and, as a matter of fact, animals brought from a 
depth of 750 feet to the surface seem to suffer no inconvenience, and 
can be kept alive for some time. Light and darkness appear also to 
be matters of indifference to a great many Invertebrata, though some 
are very sensitive to changes. 
The abyssal region of the lakes which exceed 300 feet in depth 
possesses one of the most equable climates to be found anywhere. 
Any change which takes place is secular, and confined within very 
narrow limits. The temperature may not vary one degree over a 
period of years. It is the winter temperature of the whole loch. 
The summer heat has not time to penetrate to these depths befoi-e the 
^ " Ehizopods and Heliozoa of Loch Ness," Proc. Roy. Soc. Edin., vol. xxv. p. 609, 
1905. 
