53° 
clipped only the extremity of the tarsus for a length of 
‘1 of an inch, Nevertheless, the shell did not drop off, 
on the beetle when caught shaking its leg violently. 
The specimen was brought home in a handkerchief, and 
placed after about three hours in water ; and the shell re- 
mained attached from February 18 to 23, when it dropped 
off, being stil] alive, and so remained for about a fort- 
night while in my possession. Shortly after the shell 
had detached itself, the beetle dived to the bottom of the 
vessel in which it had been placed, and having inserted 
its antenne between the valves, was again caught for a 
few minutes. The species of Dytiscus often fly at night, 
and no doubt they generally alight on any pool of water 
which they may see; and | have several times heard 
of their having dashed down on glass cucumber 
frames, no doubt mistaking the glittering surface for 
water. I do not suppose that the above weight of 6 grains 
would prevent so powerful an insect as a Dytiscus from 
taking flight. Anyhow this beetle could transport smaller 
individuals; and a single one would stock any isolated 
pond, as the species is an hermaphrodite form. Mr. 
Crick tells me that a shell of the same kind, and of about 
the same size, which he kept in water “extruded two 
young ones, which seemed very active and able to take 
care of themselves.” How far a Dytiscus could fly is not 
known; but during the voyage of the Beag/e a closely- 
allied form, namely, a Colymbetes, flew on board when 
the nearest point of land was forty-five miles distant ; 
and it is an improbable chance that it had flown from the 
nearest point. 
Mr. Crick visited the same pond a fortnight afterwards, 
and found on the bank a frog which appeared to have 
been Jately killed ; and to the outer toe of one of its hind 
legs a living shell of the same species was attached. The 
shell was rather smaller than in the previous case. The 
leg was cut off and kept in water for two days, during 
which time the shell remained attached. The leg was 
then left in the air, but soon became shrivelled; and 
now the shell being still alive detached itself. 
Mr. F. Norgate, of Sparham, near Norwich, in a letter | 
dated March 8, 1881, informs me that the larger water- 
beetles and newts in his aquarium “ frequently have one 
foot caught by a small freshwater bivalve (Cyclas cornea ?), 
and this mikes them swim about in a very restless state, 
day and night, for several days, until the foot or toe is 
completely severed.” He adds that newts migrate at 
night from pond to pond, and can cross over obstacles 
which would be thought to be considerable. Lastly, my 
son Francis, while fishing in the sea off the shores of 
North Wales, noticed that mussels were several times 
brought up by the point of the hook ; and though he did 
not particularly attend to the subject, he and his com- 
panion thought that the shells had not been mechanically 
torn from the bottom, but that they had seized the point 
of the hook. A friend also of Mr. Crick’s tells him that 
while fishing in rapid streams he has often thus caught 
small Unios. From the several cases now given, there 
can, I think, be no doubt that living bivalve shells must 
often be carried from pond to pond, and by the aid of 
birds occasionally even to great distances. I have also 
suggested in the “Origin of Species” means by which 
freshwater univalve shells might be far transported. We 
may therefore demur to the belief doubtfully expressed by 
Mr. Gwyn Jeffreys in his ‘‘ British Conchology,” namely, 
that the diffusion of freshwater shells “had a different 
and very remote origin, and that it took place before the 
present distribution of land and water.’’ 
CHARLES DARWIN 
THE FISHERY EXHIBITION AT EDINBURGH 
It has now been placed beyond doubt that this exhibi- 
“tion will prove successful, so far as a great show of 
interesting exhibits is concerned. Such exhibitions, of 
NATURE 
ee at by SP en Sf. a > Se 
‘ : ' <- Taq 
[ April 6, 1882 
course, partake in some degree of the nature of a com- 
mercial adventure—the projectors being dependent on 
the gate money to pay the expenses incurred, which are 
naturally heavy—although the prize list has been largely 
contributed to by private individuals and public bodies. 
Such an exhibition being a novelty will no doubt attract, 
from day to day, a considerable body of spectators, 
although it is deprived of many attractive features by 
reason of the place of exhibition not being fixed on the 
immediate sea-coast. It would have proved interesting, 
could the spectators have been shown the beam trawl at 
work, or have had displayed before them a suite of 
herring nets, or other items of the machinery of fish 
capture. Such apparatus will be largely displayed in the 
place of exhibition, but their effects cannot so well be 
judged as when they are seen in action. Upwards of 
seventy prizes are offered for ‘exhibits’? and “ essays’; 
the latter, indeed, seem to be a chief feature of the exhi- 
bition, and if they can be utilised for behoof of the 
public and the fisher people, some good may result. 
But, although a large number of prizes were given 
for essays at the Norwich Fishery Exhibition of last 
year, the public have not been made any the wiser 
in consequence. A very handsome surplus resulted from 
the Norwich exhibition—nearly a thousand pounds it is 
said. Why, then, has nota portion of that sum been 
devoted tu the dissemination of the knowledge contained 
in the prize essays? As regards the “ exhibits,” they can 
always be seen and understood by those who please to 
look at them, and if there are half a dozen of the same 
sort, they can be compared one with the other, and the 
decisions of the judges can be criticised, so that persons 
in search of new boats or other fishing gear, can give their 
orders for the same in the direction they think most 
suitable. But with respect to the essays the knowledge 
contained in these productions—judging from what took 
place at Norwich—will remain buried in the brains of the 
committee! Of what possible use is it to bestow a prize 
on the writer of an essay, “ On the Fish Supplies of Great 
Cities, with special reference to the best Methods of 
Catching and Packing,” if the knowledge thus obtained is 
never to become public? The prize list of the Edin- 
burgh Exhibition is rich in material for the essayist, many 
subjects of interest in the fishery world being selected for 
illustration, such as the salmon disease, oyster culture, 
the migrations and spawning of sea fish, the utilisa- 
tion of fish offal, the best methods of preserving fish 
alive for markets, the pollution of rivers, the natural his- 
tory of the herring, and twenty other subjects. In view 
of the still larger international fishery exhibition, which 
will take place in London next year, it is time this ques- 
tion of “what ought to be done with the prize essays,” 
should be ventilated and settled. Up till this moment it 
remains a blot on the Norwich exhibition that none of the 
prize essays sent there have been made public. So far as 
we know, only one of the essays has become accessible ; 
that is the essay, on the salmon disease, by Sir James 
Gibson Maitland, which, however, was printed at the 
baronet’s own expense. The exhibition at Edinburgh 
will be very much on the lines of those which took 
place some years ago at the Hague and Arcachon, except 
that the most attractive feature of the latter exhibition 
will be wanting in the well-arranged aquarium. Neither in 
Edinburgh nor in London can we hope to compete with 
the great fishery show of Berlin, which was undoubtedly 
very complete, the American national exhibits being of 
much interest. At home we have no fishery collection of 
a national kind, if we except Buckland’s Museum of 
Economic Fish Culture ; and, so far, we are at a disad- 
vantage with the United States, which possesses a very 
complete collection of fishery apparatus of all kinds, It 
is to be hoped, in the circumstances, that America will 
do for this country what it did for Germany, give us an 
opportunity of seeing and judging for ourselves how far 
