— oo. 
Nov. 23, 1882 | 
NATORE 
93 
As to the maximum depth at which they are found, Prof. 
Forel has taken them in Lake Leman as deep as 100 and even 
150 metres; at the greatest depths only Diaptomus. 
The optic nerve of those animals probably suffers from too 
bright light, and so they descend whenever the light of sun or 
moon becomes too strong ; still, they require some light to seek 
their prey. In their migrations they traverse a considerable 
thickness of water. What is the limit of light in freshwater 
lakes? The author showed in 1877, that the transparence varied 
with the season; it is much greater in winter than in summer, 
Under the most favourable conditions, a bright object sinking in 
the water of Lake Leman disappears at about 16 or 17m. depth. 
Paper sensitised with chloride of silver gave as light-limit in 
Lake Leman 45 m. in summer, and 100 m. in winter. Asper, 
using more sensitive plates (prepared with bremide of silver 
emulsion), found the actinic rays still active in the Lake of 
Zurich at 90m. and more. All this, however, does not deter- 
mine the limit of absolute obscurity for the retina, and especially 
for the optic nerve of lower animals. 
With regard to the origin of this pelagic fauna, Prof. Forel 
confidently rejects the idea of local differentiation of litttoral 
species in each lake, producing the pelagic fauna of the Jake. 
The very remarkable character of generality, the almost absolute 
identity of the pelagic entomostraca in all European lakes point 
to dissemination and mixture, 
How has this dissemination occurred? Active migration 
from one lake to another is inadmissible, considering obstacles 
and power of locomotion. On the other hand, a passive migra- 
tioa in the state of winter eggs, attached to the feathers of birds 
of passage, ducks, grebes, gulls, &c., explains the transport 
sufficiently. Pavesi has argued against this common origin and 
mode of dissemination, on account of irregularity in the pelagic 
population of different Italian lakes, certain species being absent 
in certain lakes, while they are represented in neighbouring 
lakes. But this irregularity seems to the author to correspond 
perfectly with the accidental and fortuitous character of the 
mode of dissemination referred to. ‘‘If this mode of transport 
be adiritted, the differentiation of pelagic species is no longer 
necessarily localised in the lake in which we find the animals, 
any more than inthe present geological epoch. This factis very 
important for explanation of the pelagic fauna of certain lakes 
the origin of which is comparatively modern ; for our Swiss 
lakes, the glacial epoch forms an absolute limit which prevents 
our supposing a local differentiation of ancient tertiary species, 
and their transformation into our present species ; the origin of 
the pelagic faunas of certain Italian lakes of volcanic nature, is 
still more modern. But since we are no longer limited to a 
local differentiation of autochthonous species, we find more time 
and more space for this process of differentiation.” 
Prof. Forel believes the cause of differentiation of pelagic 
fauna will be found in a combination of two facts, viz., the daily 
migrations of entomostraca, and the regular local breezes on 
large lakes. There are two such breezes in calm weather, one 
blowing from the land at night, the other from the water by 
day. Crepuscular animals of the shore region, which come to 
swim on the surface at night, are carried out ito the lake by 
the surface-current of the land breeze. Ly day the light sends 
them down, and thus they escape the surface current of the 
breeze that would bring them back to the shore. Carried each 
night further out, they become finally relegated to the pelagic 
region, Differentiation by natural selection then operates, and 
after a few generations, there remain only the admirably trans- 
parent animals and excellent swimmers we know. This differ- 
entiation once effected, the pelagic species is transported by the 
migratory birds from one country to another, from one lake to 
another, where it is multiplied, if the conditions are favourable. 
Thus we may find, even in lakes too small to po'sess an alternda- 
tion of breezes, true pelagic Entomostraca that have been 
differentiated in other larger lakes by the play of such breezes. 
The differentiation of most pelagic species may thus be easily 
accounted for. 
There are two species, however, the author points out, whose 
origin is not so explained ; these are the most beautiful and 
interesting of pelagic Entomostraca: Leftodora hyalina and 
Bythotrephes longimanus, These two Cladocera have no known 
parentage in the freshwater species forming either the shore 
fauna of lakes or the marsh or river fauna, We must, with 
Pavesi, seek a marine origin for them. Aythotrephes probably 
descended from a common ancestor with Podon, its nearest 
parent, and the Zef/odora from a primitive Daphnis. 
How did the passage from salt to fresh water take place? 
Pavesi supposes closure of a fjord and gradual transformation 
of the lake water in conseqnence. Prof. Forel further suggests 
as possible, passive migration and successive transport to lagoons 
less and less salt ; and there may have been other ways. We 
have not the elements for settling the question. ‘But the 
adaptation to fresh water once accomplished, the dissemination 
of these forms of marine origin has certainly taken place like 
that of other pelagic fresh-water forms, and those two species 
have so been transported into lakes which have never had direct 
communication with the sea.” 
There are evident analogies, Prof. Forel remarks in closing, 
between the lacustrian and the marine pelagic fauna ; the differ- 
ences appear chiefly in relative size and proportions. In the sea 
all is on a large scale; in lakes, on a small; the number of 
species and of individuals, the size, the extent of the migrations, 
the area of extension. But, with this exception, the general 
laws are the same in the two analogous faunas. 
UNIVERSITY AND EDUCATIONAL 
INTELLIGENCE 
Four chairs in the University College, Dundee, have been 
filied up as follows :—Mr. Steggall, Fielden Lecturer in Mathe- 
matics, in Owens College, Manchester, was appointed Professor 
of Mathematics; Mr. Carnelly, Professor of Chemistry in Firth 
College, Sheffield, was appointed Professor of Chemistry ; Mr. 
Ewing, Professor of Engineering in the University of Tokio, 
Japan, was appointed to the Chair of Engineering; and Mr. 
Thomas Gilray, M.A., Head Master in English at Glasgow 
Academy, to tue Chair of English Literature and Modern His- 
tory. The salary guaranteed to each professor is 500/. 
+ THE University of Ziirich will, at the end of the current 
winter term, celebrate the fiftieth anniversary of its foundation, 
SCIENTIFIC SERIALS 
The Fournal of Anatomy and Physiology, vol.-xvii. Part 1, 
October, 1882, contains -—On the lymphatics of the walls of the 
larger blood-vessels, and lymphatics, by Drs. George and Eliza- 
beth Hoggan.—On micrococcus poisoning, by Dr. A. Ogston. 
—On omphalo-mesenteric remains in mammals, by Dr, W. 
Allen.—On the action of saline cathartics, by Dr. M. Hay.—On 
a hitherto undescribed fracture of the Astragalus, by Dr. F. J. 
Shepherd.—On a secondary astragalus in the human foot, by 
Prof. W. Turner.—Note on the rectus abdominalis et sternalis 
muscle, by Dr. G. E. Dobson.—On a case of ectopia vesice, 
&e., ina newly-born infant, by Dr. F. Ogston.—On nickel and 
cobalt ; their physiological action on the animal organism. Part 
i., Toxicology, by Dr. T. P. A. Stuart.—A kerato-thyro-hyoid- 
muscle as a variation in human anatomy, by S. G. Shattock.— 
On Cesalpino and Harvey, by Prof. Humphry. 
The Proceedings of the Linnean Society of New South Wales, 
vol, vii. part 1 (Sydney, 1882), contains: Wm. A. Haswell, on 
the structure of the paired fins of Ceratodus (plate 1).— Notes on 
the anatomy of 4airhinus insolitus and Turacena crassirostris. 
—Wnm. Macleay, on Port Jackson Pleuronectidz, with descrip- 
tions of new species; on the fishes of Palmer River; on an 
Alpine species of Galaxias.—E. P. Ramsay, the zoology of the 
Solomons, Part IV. ; on a new species of Mus from Ugi Island; 
contributions to Australasian oology (plates 3-5) ; on the zoology 
of Lord Howes Island ; on Afogon guntheri of Castelnau ; on 
some Fijian bird’s eggs. —Alex. Morton, notes of a cruise to the 
Solomons.—Prof. F, W. Hutton, note on Sossarina petterdt ; 
list of New Zealand freshwater shells.—Rev. Dr. Wools, the 
plants of New South Wales, No. 8.—Rev. J. E. T. Woods, 
botanical notes on Queensland; on a new species of Stomo- 
pneustes, and a new variety of Aipponce variegata ; on fossil 
plants of Queensland.—J. Brazier, fluviatile shells of New 
South Wales ; a list of Cypraeidee of the Victorian coast.—Wm. 
Mitten, on some Polynesian mosses.—Rey. C. Kalchbrenner, 
new Australian fungi.—Dr. J. C. Cox, on the edible oysters of 
Australia. 
Journal and Proceedings of the Royal Society of New South 
Wales, vol. 15, 1882, contains: On the climate of Mackay, by 
H. L. Roth.—Notes of a journey on the Darling, by W. E. 
Abbott.—The astronomy of the Australian aborigines, by Rev. 
P. MacPherson.—On the spectrum of the recent comet; on 
