ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 
161 
7. G-eneral. 
Temperature as a Factor in the Distribution of Marine Animals.*— 
Dr. 0. Maas points out that in the discussion of the influence of tempe- 
rature on marine animals, no sufficient distinction has hitherto been 
made between three classes of facts — (1) between the animals of the 
plankton, the benthos, and the nekton ; (2) between the vertical and 
horizontal differences of temperature; and (3) between eurythermal 
animals which can stand great differences of temperature and the steno- 
thermal which cannot. Eurythermal animals must not be appealed 
to in proof of anything regarding temperature. For the stenothermal 
animals the average temperature of a locality is of small zoogeogra- 
phical value, while the extent of variation is the most important factor. 
The nekton animals are more eurythermal ; otherwise their power of 
swimming, which brings them into very different temperatures, would 
be of no use to them. It is possible to make a geographical distribution 
of the animals of the open ocean chiefly because of the currents. The 
Geryonidae are found in every ocean basin not to go beyond a certain 
north and south latitude. In the scale of plankton animals, they occupy 
a similar portion of the map to the corals of the benthos. 
Fauna of Lakes.']' — M. F. A. Forel, who has devoted a large amount 
of time to lacustrine zoology, has a general essay on this subject. He 
points out that the whole fauna has immigrated into the lake. The 
littoral fauna arises directly from river or marsh species brought to the 
lake by streams or other methods. The pelagic fauna is remarkable for 
its cosmopolitan character, the same species are found always identical 
in all the lakes of the same continent and even on different continents. 
A number of species are common to the Old and New World. This 
dissemination is effected by the transport of germs, and, perhaps, even 
of living animals, on the skins of migratory birds. The deep fauna of 
the lake has been differentiated in the lake itself ; the deep fauna of one 
lake can have no direct contact with the deep regions of other lakes. 
The fauna has probably arisen partly by some individuals of the littoral 
species being by some accident carried, or frightened to actively emi- 
grate into the deep. Where they survived the transplantation they 
became adapted to the fresh conditions of the surrounding medium. 
Other individuals are probably derived from subterranean waters which 
open into the deep region of the lake, and which have found the condi- 
tions of the surrounding medium sufficiently similar to that of their 
primitive habitat to be able to dwell there and reproduce their kind. 
Origin of Irish Land and Freshwater Fauna.f— Dr. R. F. Scharff 
discusses the origin of the Irish Land and Freshwater Fauna, and comes 
to the conclusion that Ireland was in later Tertiary times connected 
with Wales in the south and Scotland in the north, whilst a freshwater 
lake occupied the present central area of the Irish Sea. The southern 
connection broke down at the beginning of the Pleistocene period, the 
northern connection following soon after. There is no evidence of any 
subsequent land connection between Great Britain and Ireland. 
* Rep. Brit. Assoc., 1894, pp. 687-8. 
f Arch. Sci. Phys. et Nat., xxxii. (1894) pp. 588-605. 
i Proc. Roy. Irish Acad., iii. (1894) pp. 479-85. 
1895 
M 
