PEARLS AND PARASITES
PEARLS & PARASITES
BY ARTHUR E. SHIPLEY
OF CHRIST’S COLLEGE, CAMBRIDGE; M.A., HON. D.SC., F.R.S.
WITH ILLUSTRATIONS
LONDON
JOHN MURRAY, ALBEMARLE STREET, W.
1908
TO MY SISTER
E. D. H.
PREFACE
Most of the following essays have appeared in the pages of the
_Quarterly Review_, and I am greatly indebted to the editor and to the
proprietor of that periodical for permission to reprint them. The
article on ‘The Infinite Torment of Flies’ is an address I delivered
before the British Association at Pretoria in 1905, and the eighth essay
appeared in _Science Progress_.
As far as possible I have tried to avoid the use of long words, and thus
escape the censure of recent critics in the _Times_; but I fear I have
not altogether succeeded, and my excuse must be that with new
discoveries new conceptions arise, and these conceptions require new
names, or we cannot talk or write about them with any precision.
The essay dealing with zebras and hybrids was the first to be written,
and appeared before the rediscovery of Mendel’s remarkable work, and
must be regarded as a pre-Mendelian contribution to a subject which has
recently, in connexion with the Deceased Wife’s Sister Bill, again
aroused attention. Had it been written later the language and the
attitude taken would have been modified by recent research.
In the inquiry into the aims and finance of Cambridge University--the
only essay which does not deal with questions of economic zoology--I
have had the great advantage of the collaboration of Mr. H. A. Roberts,
the Secretary of the Cambridge University Association. But for his help
I fear I should have lost my way in the intricate mazes of the
University accounts.
For the care he has taken in making the Index, I owe thanks to Mr. G. W.
Webb, of the University Library.
A. E. S.
CHRIST’S COLLEGE,
CAMBRIDGE.
_March 10, 1908._
CONTENTS
PAGE
PEARLS AND PARASITES 1
THE DEPTHS OF THE SEA 16
BRITISH SEA-FISHERIES 42
ZEBRAS, HORSES, AND HYBRIDS 73
PASTEUR 101
MALARIA 129
‘INFINITE TORMENT OF FLIES’ 155
THE DANGER OF FLIES 174
CAMBRIDGE 183
INDEX 217
LIST OF ILLUSTRATIONS
FACING PAGE
MATOPO 84
TUNDRA (AN ICELAND PONY), HER FOAL, CIRCUS GIRL (BORN
1898), AND HER HYBRID-FOAL, SIR JOHN (BY MATOPO),
WHEN A MONTH OLD (BORN 1899) 86
ROMULUS 92
MATOPO 92
ROMULUS 96
FIG. 1.--THE PARASITE OF TERTIAN FEVER, HÆMAMŒBA VIVAX
(ROSS). HIGHLY MAGNIFIED 136
FIG. 2.--VARIOUS STAGES WHICH THE PARASITE OF THE ÆSTIVO-AUTUMNAL
FEVER, HÆMOMENAS PRÆCOX(ROSS), PASSES THROUGH IN THE BODY OF
THE MOSQUITO ANOPHELES. MAGNIFIED 2,000 TIMES. AFTER ROSS
AND FIELDING-OULD 136
FIG. 3.--FORMATION OF THE BLASTS OF HÆMOMENAS PRÆCOX
(ROSS) WITHIN THE BODY OF THE MOSQUITO ANOPHELES.
MAGNIFIED 2,000 TIMES. AFTER ROSS AND FIELDING-OULD
144
_ANOPHELES MACULIPENNIS._ MALE, IN CHARACTERISTIC
ATTITUDE 146
_ANOPHELES MACULIPENNIS._ FEMALE 146
BIBLIOGRAPHY
‘Report to the Government of Ceylon on the Pearl-Oyster Fisheries of the
Gulf of Manaar.’ By W. A. Herdman, F.R.S. Parts I. and II. Published by
the Royal Society. London, 1904.
‘On the Origin of Pearls.’ By H. Lyster Jameson. Proceedings of the
Zoological Society of London, 1902.
‘Aus den Tiefen des Weltmeeres.’ By C. Chun. Jena: Gustav Fischer, 1900.
‘Tierleben der Tiefsee.’ By O. Seeliger. Leipzig: Wilhelm Engelmann,
1901.
‘Report of the Scientific Results of the Voyage of H.M.S. _Challenger_.’
Edited by the late Sir C. Wyville Thomson and John Murray. A Summary of
the Scientific Results. Published by Order of Her Majesty’s Government,
1885.
‘La Vie au Fond des Mers.’ By H. Filhol. Paris: G. Masson, 1885.
‘The Fauna of the Deep Sea.’ By Sydney J. Hickson. London: Kegan Paul,
Trench, Trübner and Co., 1894.
‘British Fisheries: their Administration and their Problems.’ By James
Johnstone. London: Williams and Norgate, 1905.
‘An Examination of the Present State of the Grimsby Trawl Fishery, with
Especial Reference to the Destruction of Immature Fish.’ By E. W. L.
Holt. _Journal of the Marine Biological Association_, vol. iii.
Plymouth, 1895.
_Journals of the Marine Biological Association of the United Kingdom_,
vols. i.-vii. Plymouth.
‘Conseil Permanent International pour l’Exploration de la Mer. Rapports
et Procès Verbaux,’ vol. iii. Copenhagen.
‘Fishery Board for Scotland. Report on the Fishery and Hydrographical
Investigations in the North Sea and Adjacent Waters, 1902-1903.’ [Cd.
2612.] London, 1905.
‘Marine Biological Association. First Report on the Fishery and
Hydrographical Investigations in the North Sea and Adjacent Waters
(Southern Area), 1902-1903.’ [Cd. 2670.] London, 1905.
‘Annual Reports of the Inspectors of Sea-Fisheries for England and
Wales.’ London, 1886-1905.
‘The Penycuik Experiments.’ By J. C. Ewart. London and Edinburgh: A. and
C. Black, 1899.
‘Experimental Investigations on Telegony.’ A paper read before the Royal
Society, London, June 1, 1899. By Professor J. C. Ewart.
‘La Vie de Pasteur.’ Par René Vallery-Radot. Paris: Hachette, 1900.
‘Pasteur.’ By Percy Frankland and Mrs. Percy Frankland. (Century Science
Series.) London: Cassell, 1898.
‘The Soluble Ferments and Fermentation.’ By J. Reynolds Green.
(Cambridge Natural Science Manuals.) Cambridge University Press, 1899.
‘Micro-organisms and Fermentation.’ By Alfred Jörgensen. Translated by
A. K. Miller and A. E. Lennholm. Third edition. London: Macmillan, 1900.
‘Lectures on the Malarial Fevers.’ By William Sydney Thayer, M.D.
London: Henry Kimpton, 1899.
‘On the Rôle of Insects, Arachnids, and Myriapods as Carriers in the
Spread of Bacterial and Parasitic Diseases of Man and Animals. A
Critical and Historical Study.’ By George H. F. Nuttall, M.D., Ph.D.
‘Johns Hopkins Hospital Reports,’ vol. viii.
‘Instructions for the Prevention of Malarial Fever.’ Liverpool School of
Tropical Medicine. Memoir I. Liverpool: University Press, 1899.
‘Report of the Malaria Expedition of the Liverpool School of Tropical
Medicine and Medical Parasitology.’ By Ronald Ross, D.P.H., M.R.C.S.; H.
E. Annett, M.D., D.P.H.; and E. E. Austen. Liverpool School of Tropical
Medicine. Memoir II. Liverpool: University Press, 1900.
‘A System of Medicine, by many Writers.’ Edited by Thomas Clifford
Allbutt, M.A., M.D., LL.D., vol. ii., 1897; vol. iii., 1897. London:
Macmillan and Co.
‘A Handbook of the Gnats and Mosquitoes.’ By Major George M. Giles,
I.M.S., M.B., F.R.C.S. London: John Bale, Sons, and Danielsson, Limited,
1900.
‘Reports to the Malaria Committee, Royal Society, 1899 and 1900.’ By
various authors. London: Harrison and Sons, 1900.
Proceedings of the Boston Society of Natural History, vol. xvi., 1874.
U.S.A. Department of Agriculture, Division of Entomology, Bulletin 4,
new series.
‘Manchester Memoirs,’ vol. li., 1906, p. 1; _Quarterly Journal of
Microscopical Science_, vol. li., 1907, p. 395.
‘Endowments of the University of Cambridge.’ Edited by John Willis
Clark, M.A., Registrar of the University of Cambridge. Cambridge:
University Press, 1904.
‘Report of a Meeting held at Devonshire House on January 31, 1899, to
inaugurate the Cambridge University Association.’ Cambridge: University
Press, 1899.
‘Statements of the Needs of the University.’ Cambridge: University
Press, 1904.
‘University Accounts for the Year ended December 31, 1904.’ _Cambridge
University Reporter_, March 17, 1905.
‘Abstracts of the Accounts of the Colleges.’ _Cambridge University
Reporter_, February 10, 1905.
PEARLS AND PARASITES
_Know you, perchance, how that poor formless wretch--_
_The Oyster--gems his shallow moon-lit chalice?_
SIR EDWIN ARNOLD.
Certain Eastern peoples believe that pearls are due to raindrops falling
into the oyster-shells which conveniently gape to receive them.
‘Precious the tear as that rain from the sky
Which turns into pearls as it falls on the sea,’
as the poet Moore writes. This belief is of ancient origin, and is
probably derived from classical sources, since Pliny tells us that the
view prevalent in his time was that pearls arise from certain secretions
formed by the oyster around drops of rain which have somehow effected an
entrance into the mantle cavity of the mollusc. Probably this theory of
the origin of pearls has ceased to be held for many centuries except in
the East, where tradition has always received more credit than
experiment. In the West it has long been known that pearls are formed as
a pathological secretion of the mineral arragonite, combined with a
certain amount of organic material, formed by the oyster or other
mollusc around some foreign body, whose presence forms the irritant
which stimulates the secretion. This secretion is of the same chemical
and mineralogical nature as the mother-of-pearl which gives the inside
of the shell of so many molluscs a beautiful iridescent sheen.
An oyster-shell consists of three layers, the outermost termed the
_periostracum_, the middle the _prismatic layer_, and the innermost the
_nacreous layer_. Everywhere the shell is lined by the mantle,
consisting of a right and left fold or flap of the skin, which is in
contact with the nacreous layer all over the inside of the shell. The
edge of the mantle is thickened and forms a ridge or margin; and it is
this edge which secretes the two outer layers. This permits the shell to
grow at its edge whilst the rest of the mantle secretes all over its
surface the nacreous or pearly layer. The relative thickness of these
three layers varies very greatly. In the fresh-water mussel (_Unio_) the
nacreous layer is many times thicker than the two outer layers put
together; and such nacreous shells are usually associated with molluscs
which are known to represent very ancient or ancestral species. It is
also the layer which disappears most readily as the specimens become
fossilized; and in fossil Mollusca it is often represented by mere
casts, which fill the position it once occupied.
The fact that the nacre is deposited by the whole surface of the mantle
has been appreciated by the Chinese. By inserting little flattened
leaden images of Buddha between the mantle and the shell, and leaving
the oyster at rest for some time, the image becomes coated with
mother-of-pearl and incorporated in the substance of the shell; and in
this way certain little joss figures are produced. This industry is said
to support a large population in some coast districts of Siam.
The nacre, then, is produced by the outermost layer of the mantle or
fleshy flap that lines the shell--the external epithelium; and, if a
foreign body gets between this epithelium and the shell, the mantle
will, in order to protect itself, secrete a pearly coat around it. But
valuable pearls are not those which are partially or wholly fused with
the shell, but those which lie deep in the tissues of the body; and they
are probably formed in the following manner: The intrusive, irritant
body forms a pit in the outer surface of the mantle; this pit deepens,
and at first remains connected with the outside by a pore; ultimately
the pore closes, and the bottom of the pit becomes separated as a small
sac free from all connexion with the outside. The sac now sinks into the
tissues of the oyster, enclosing in it the foreign body. It will be
noticed that the inside of the sac is lined by and is derived from the
same tissue or epithelium as covers the outside of the mantle. Now this
epithelium continues to do what it has always been in the habit of
doing; that is, it secretes a nacreous substance all round the intrusive
particle. Layer after layer of this nacre is deposited, and thus a pearl
is formed. At first the layers will conform roughly to the outline of
the embedded body, but later layers will smooth over any irregularities
of the nucleus around which they are deposited, and a spheroidal or
spherical pearl is produced. If the irregularities are too pronounced,
an irregular pearl is formed; and such pearls, on merely æsthetic
grounds, command a lower price.
It is thus clear that pearls are formed around intrusive foreign bodies;
and until comparatively recently these bodies were thought to be
inorganic particles, such as grains of sand. Recent research has,
however, shown that this is seldom the case, and that as a rule the
nucleus, which must be present if a pearl is to be formed, is the larva
of some highly-organized parasite whose life-history is certainly
complicated but as yet is not completely known. The knowledge, however,
which we already possess enables us to do much to ensure steady success
in a very speculative industry; and with complete knowledge there is no
reason why pearl fisheries should not be under as good control as oyster
fisheries now are.
It was about fifty years ago (1857-1859) that the problem of the Ceylon
pearl-oyster fishery was first attacked in a thoroughly scientific
spirit by a certain Dr. Kelaart. His reports to the Government of the
island contain the following suggestive sentences:
‘I shall merely mention here that M. Humbert, a Swiss zoologist,
has, by his own observations at the last pearl fishery,
corroborated all I have stated about the ovaria or genital glands
and their contents; and that he has discovered, in addition to the
Filaria and Circaria (_sic_), three other parasitical worms
infesting the viscera and other parts of the pearl-oyster. We both
agree that these worms play an important part in the formation of
pearls; and it may be found possible to infect oysters in other
beds with these worms, and thus increase the quantity of these
gems. The nucleus of an American pearl drawn by Möbius is nearly of
the same form as the Circaria found in the pearl-oysters of Ceylon.
It will be curious to ascertain if the oysters in the Tinnevelly
banks have the same species of worms as those found in the oysters
on the banks off Arripo.’
Unfortunately Dr. Kelaart died shortly after making this report, leaving
his investigations incomplete.
Some seven years before, in 1852, Filippi had shown that the pearls in
our fresh-water mussel (_Anodonta_) were formed by the larvæ of a fluke
(a trematode), to which he gave the name of _Distomum duplicatum_. Many
students of elementary biology, as they painfully try to unravel the
mystery of molluscan morphology, must have come across small pearls in
the tissues of the fresh-water mussels (_Unio_ or _Anodonta_); but these
are said to have less lustre and to be more opaque than the sea pearl;
so the pearl fisheries of the Welsh and Scotch rivers are falling into
disuse. Our ancestors, however, thought otherwise. Less than fifty years
ago the Scotch fisheries brought in some £12,000 a year; and a writer of
the early part of the eighteenth century describes Scotch pearls as
‘finer, more hard and transparent than any Oriental.’ British pearls
were highly thought of by the Romans. Pliny and Tacitus mention them;
and Julius Caæsar is said to have dedicated a breastplate ornamented
with British pearls to Venus Genitrix. Fresh-water pearls are still
‘fished’ with profit in Central Europe; but the Governments of Bavaria,
Saxony, and Bohemia watch over the industry and only grant a licence to
fish any stretch of water about once in twelve years--a restriction
which, had it been imposed on our fisheries, might have saved a
vanishing industry.
In 1871 Garner showed that the pearls in the edible mussel (_Mytilus
edulis_), which is largely used for bait upon our coasts, were formed
round the larvæ of a fluke, a remote ally of the liver-fluke that causes
such loss to our sheep-breeders. This origin of pearls has been more
completely followed out by Mr. Lyster Jameson. Nor must we forget to
mention the researches of Giard (1897) and Dubois (1901) in the same
subject. We know the life-history of the organism forming pearls in this
edible mussel more completely than we do that of any other pearl-forming
parasite; and, before returning to the Ceylon pearls, we will briefly
consider it.
Mr. Lyster Jameson finds that the pearls of the _Mytilus_ are formed
around the cercaria or larval form of a fluke which, in its adult
stages, resides in the intestine of the scoter (_Œdemia nigra_), and
was originally described from the eider-duck (_Somateria mollissima_) in
Greenland and named _Leucithodendrium somateriæ_, after its first known
host. The cercaria larvæ of these flukes form the last stage in a
complex series of larval forms which occur in the life-history of a
trematode or fluke, and they differ from the adult in two points--their
generative organs are not fully developed, and they usually have a tail;
but this organ is wanting in our pearl-forming cercaria, called a
cercariæum by Mr. Jameson. Such a larva has only to be swallowed by a
scoter to grow up quickly into the adult trematode capable of laying
eggs. Now this bird, called by the French fishermen the ‘cane moulière,’
is the greatest enemy to the mussel-beds; it is not only common around
the French mussel-beds of Billiers (Morbihan), but occurs in numbers at
the mouth of the Barrow channel, close to our English pearl-bearing
mussel-beds. With its diving habits it destroys and eats large
quantities of the mollusc. Those cercariæ which are already entombed in
a pearl cannot, of course, grow up into adults, even if they gain
entrance to the alimentary canal of the scoter; but those that are not
ensheathed may do so. Further, the fluke may possibly live in other
hosts where no pearl is formed. At any rate, there seems no lack of
larvæ successful in their struggle to attain maturity, for it has been
calculated that the alimentary canal of an apparently healthy scoter may
harbour as many as six thousand adult flukes.
Thus there are two courses open to the cercaria when it has once found
its way into the mussel; it either forms the nucleus of a pearl and
perishes, or it is swallowed by a scoter, becomes adult, and prepares to
carry on the race. But how do the cercariæ make their way into the
mussel, and whence do they come? At present their birth, like that of
Mr. Yellowplush, is ‘wrapped up in a mistry.’ We may presume that the
eggs make their way out of the scoter into the sea-water, and that there
they hatch out a free-swimming larva, which, after the manner of
trematodes, swims about looking for a suitable host. Within this host
it would come to rest and begin budding off numerous secondary larvæ, in
which stage it may assume considerable size and becomes known as a
_sporocyst_. No one, however, has seen the eggs hatch, or the
free-swimming larva; but Mr. Jameson produces evidence to show that the
sporocyst stage occurs in two other common molluscs--viz., in a clam
(_Tapes decussatus_) and in the common cockle (_Cardium edule_). The
former mollusc abounds in the black gravelly clay which forms the bottom
of the mussel-beds at Billiers; and every specimen out of nearly two
hundred examples investigated by Mr. Jameson was found to be infested
with sporocysts containing larvæ closely resembling those which act as
pearl-nuclei in the edible mussel. Exactly similar sporocysts were found
in about fifty per cent. of the common cockles examined in the Barrow
channel, where the species _Tapes decussatus_ does not occur.
Within the sporocyst certain secondary larvæ are formed, as is habitual
with the flukes. These secondary larvæ are the cercariæ; and it is in
this stage that the animal makes its way into the pearl-mussel and
ultimately forms the nucleus of a pearl. Precisely how it leaves the
sporocyst and the first host--_i.e._, the _Tapes_ or _Cardium_--is not
known. Certain experiments made by Jameson, who placed mussels which he
thought were free from parasites in a tank with some infected _Tapes_,
are not quite conclusive, and have been ably criticized by Professor
Herdman. It is true that, when examined later, the mussels were well
infected; but it was not definitely shown that they were not infected at
the start; and further, the numbers used were too small to justify a
very positive conclusion. Still, on the whole, it may safely be said
that life-history of the organism which forms the pearls in _Mytilus
edulis_ probably involves three hosts: the scoter, which contains the
mature form; the _Tapes_ or _Cardium_, which contains the first larval
stage; and the mussel, which contains the second larval stage, which
forms the pearl.
Recently Professor Dubois has been investigating the origin of pearls in
another species of _Mytilus_ (_M. galloprovincialis_) which lives on the
French Mediterranean littoral. The nucleus of this pearl is also a
trematode, but of a species different from that which infests the edible
mussel. The interest of Professor Dubois’ work, however, lies in the
fact that he claims to have infected true Oriental pearl-oysters by
putting them to live with his Mediterranean mussels. He fetched his
oysters, termed ‘Pintadin,’ from the Gulf of Gabes in Southern Tunis,
where they are almost pearlless--one must open twelve to fifteen hundred
of these to find a single pearl--and brought them up amongst the
mussels. After some time had elapsed they became so infected that three
oysters opened consecutively yielded a couple of pearls each. These
observations, however, require confirmation, and have been adversely
criticized by Professor Giard.
To return to the Ceylon pearls. The celebrated fisheries lie to the
north-west of the island, where the shallow plateaux of the Gulf of
Manaar afford a fine breeding-place for the pearl-oyster. The
pearl-oyster is not really an oyster, but an allied mollusc known as
_Margaritifera vulgaris_. It lives on rocky bottoms known locally as
paars. The fisheries are very ancient and have been worked for at least
2,500, perhaps for 3,000 years. Pliny mentions them, but he is,
comparatively speaking, a modern. The Cingalese records go much farther
back. In 550 B.C. we find King Vijaya sending his Indian father-in-law
pearls of great price; and there are other early records. From the
eighth to the eleventh century of our era the trade seems to have been
chiefly in the hands of the Arabs and Persians; and many references to
it occur in their literature. Marco Polo (1291) mentions the pearls of
the kings of Ceylon; and in 1330 a friar, one Jordanus, describes 8,000
boats as taking part in the fishery. Two centuries later, a Venetian
trader named Cæsar Frederick, crossed from India to the west coast of
Ceylon to observe the fishery; and his description might almost serve
for the present day, so little do habits alter in the East.
The records of the Dutch and English fisheries are naturally more
complete than those of their predecessors. The last Dutch fishery was in
1768, and the first English was in 1796, before the fall of Colombo. The
fishery is not held every year, but at irregular intervals; and
sometimes these intervals have been long. For instance, the oysters
failed between 1732 and 1746, and again between 1768 and 1796, under the
Dutch régime, and from 1837 to 1854 under the English. On the other
hand, the fishing is sometimes annual; recently, it took place with
great success in 1887 and the four following years, culminating in the
record year 1891, when the Government’s share of the spoil amounted to
close upon one million rupees. After this there was a pause till 1903,
when the fishery became annual.
The Lieutenant-Governor, Sir Everard im Thurn, now Governor of Fiji, has
given a lively account of the fishing scene. He tells us that every
year, in November, a Government official visits the oyster-beds, takes
up a certain number of oysters, examines them for pearls, and submits
his results to certain Government experts. If, as they have done
recently, these experts pronounce that there will be a fishing, this
information is at once made known; and, partly by advertisement, but
probably more by passing the word from man to man, the news rapidly
spreads throughout India, up the Persian Gulf, and to Europe. In the
meantime preparations on a large scale have to be made.
‘On land, which is at the moment a desert, an elaborate set of
temporary Government buildings have to be erected for receiving and
dealing with many millions of oysters and their valuable if minute
contents. Court-houses, prisons, barracks, revenue offices,
markets, residences for the officials, streets of houses and shops
for perhaps thirty thousand inhabitants, and a water-supply for
drinking and bathing for these same people, have to be arranged
for. Lastly, but, in view of the dreadful possibility of the
outbreak of plague and cholera, not least, there are elaborate
hospitals to be provided.’
By March or April some hundreds of large fishing vessels have assembled
at Manaar; and a population which varies during the next two months
between 25,000 and 40,000 souls has gathered together.
The fishing-boats leave early in the morning for their respective
stations; and, on reaching them, the Arab and Indian divers descend,
staying under water from fifty to eighty seconds, and eagerly scooping
up the oysters and depositing them in baskets slung round their necks.
By midday the divers are worn out; and at noon a gun is fired from the
master-attendant’s vessel as a signal for return. The run home may take
some hours, according to the distance and the wind; and it is during
this time that a considerable number of pearls are said to be
abstracted. The men on the boats are occupied with the sorting of the
oysters and cleaning them of useless stones, seaweed, and other objects
which are gathered with them. The finest pearls lie just within the
shell, embedded in the edge of the mantle; and these readily slip out
and are concealed about the person of the finder. The Government does
what it can to check peculation and keep a guard on each boat; but, in
spite of all its efforts, there seems no doubt that many of the ‘finest,
roundest, and best-coloured pearls’ pass into the possession of those
who have no right to them.
On reaching the shore the oysters are carried to the Government building
or ‘Kottus,’ a vast rectangular shed, where they are divided into three
heaps; two of these fall to the Government, and the third belongs to the
divers. This latter share the divers sell as soon as they quit the
‘Kottus,’ sometimes parting with dozens to one buyer, and sometimes
selling as few as two or one. In the meantime the Government’s
two-thirds have been counted and are left for the night. At nine o’clock
in the evening these oysters are put up to auction. The Government agent
states how many oysters there are to dispose of, and then sells them in
lots of one thousand. Some rich syndicates will perhaps buy as many as
50,000 at prices which fluctuate unaccountably during the evening.
Within a short time the price will inexplicably drop from thirty-five
rupees to twenty-two rupees a thousand, and may then rise again as
suddenly and inexplicably as it sank. Early in the morning each
purchaser removes his shells to his own private shed, where for a week
they are allowed to rot in old canoes and other receptacles for water,
and are then searched for pearls. For a couple of months this great
traffic goes on, until the divers are thoroughly exhausted, and the camp
melts away.
Owing to the continuous failure of the fishery for ten years from 1891,
the Government determined to call in the aid of experts. In the spring
of 1901 Professor Herdman of Liverpool was asked by the Colonial Office,
then under the direction of Mr. Chamberlain, to visit Ceylon and to
report upon the state of the fishery. He reached Colombo early in 1902.
He was fortunate in taking out an exceptionally well qualified assistant
in Mr. J. Hornell. After a thorough examination of the fishing-grounds,
Professor Herdman reported to the Government of Ceylon as follows:
‘The oysters we met with seemed, on the whole, to be very healthy.
There is no evidence of any epidemic or of much disease of any
kind. A considerable number of parasites, both external and
internal, both protozoan and vermean, were met with; but that is
not unusual in molluscs, and we do not regard it as affecting
seriously the oyster population.
‘Many of the larger oysters were reproducing actively. We found
large quantities of minute “spat” in several places. We also found
enormous quantities of young oysters a few months old on many of
the paars. On the Periya paar the number of these probably amounted
to over a hundred thousand million.
‘A very large number of these young oysters never arrive at
maturity. There are several causes for this. They have many natural
enemies, some of which we have determined. Some are smothered in
sand. Some grounds are much more suitable than others for feeding
the young oysters, and so conducing to life and growth. Probably
the majority are killed by overcrowding.
‘They should therefore be thinned out and transplanted. This can be
easily and speedily done, on a large scale, by dredging from a
steamer at the proper time of the year, when the young oysters are
at the best age for transplanting.
‘Finally, there is no reason for any despondency in regard to the
future of the pearl-oyster fisheries if they are treated
scientifically. The adult oysters are plentiful on some of the
paars, and seem for the most part healthy and vigorous; while young
oysters in their first year, and masses of minute spat just
deposited, are very abundant in many places.’
The chief causes of the failure of the fisheries, at any rate the chief
causes which can be dealt with by man, are overcrowding and
over-fishing. It might be supposed that these factors would counteract
each other; but it must be remembered that they become effective at the
two opposite poles of the oyster’s existence, which is thought to cover
five, six, or seven years. The overcrowding takes place when the oyster
is quite young and hardly fixed on the submerged reefs, whilst the
over-fishing takes place when the animal is fully matured and perhaps
growing old. The fact that Professor Herdman and Mr. Hornell conveyed
the young oysters from Manaar in the north of the island by boat to
Colombo and then on by train to Galle in the south, and there succeeded
in rearing them, shows that there would be little difficulty in
artificially rearing oysters in convenient localities and then
transplanting them to such fishing-grounds as show danger of depletion.
With regard to over-fishing, if the grounds are under the charge of a
trained zoologist there is no reason why this should go on.
When Professor Herdman was called in to advise the Government, he saw at
once that it was the oyster that had failed in the last ten years, not
the pearls within the oysters. Microscopic examination of thin sections
made through decalcified pearls showed that they are almost in all cases
deposited around a minute larval cestode or tapeworm. These larvæ make
their way into the oyster, and the irritation they set up induces the
formation of the pearl, just as was the case with the cercaria-formed
pearls of the mussel. Where do these larvæ come from? We cannot say with
absolute certainty. Older specimens of tapeworms belonging to the new
species, _Tetrarhynchus unionifactor_, also live in the oyster; and it
may be that, were a larva to escape entombment in a pearl, it would grow
up into one of these. But even these never become mature in the oyster;
to attain sexual maturity they must be swallowed by a second host. What
is the second host of the pearl-forming cestode? This question we are
only recently able to answer, and here, again, without absolute
certainty. I have recently described the adult form of _T. unionifactor_
from a large ray, _Rhinoptera javanica_. In this fish, which feeds
largely on oysters, the cestodes exist in swarms in the stomach, and the
eggs make their way from the fish into the oysters, and there some of
them grow up, but most of them perish in their pearly casket. If, as I
believe, this is the history of the pearl-forming organism, we must
regard the _Rhinoptera_ as a friend to the industry, and not, as
hitherto, an enemy which helps to destroy the oyster-beds.
The discovery of the cestode larva as a real cause of pearl-formation
received an interesting confirmation shortly after it had made it. M. G.
Seurat, working independently at Rikitea on the island of Mangareva, in
the Gambier group, discovered a very similar larva in the local
pearl-oyster around which pearls are formed; this larva, if we may judge
from pictures, is almost certainly the same as the one from Ceylon.
Professor Giard regards it as belonging to a tapeworm of the genus
_Acrobothrium_; and, if he be right, then Professor Herdman’s larva is
an _Acrobothrium_ too. We have so little knowledge of the early forms of
cestodes that we cannot accept this attribution as final. We may,
however, hope for further information, for a French zoologist, M.
Boutan, started some little time ago for the East to work at the
problem; Mr. Hornell is still at work in Ceylon; and Mr. C. Crossland,
who has had much experience in marine work in the tropics, has been
appointed, at the request of the Soudan Government, to investigate the
pearl-oyster beds of the Red Sea. Finally Dr. Willey, of the Colombo
Museum, has recently described similar larvæ in the pearls of the
‘window-pane’ oyster, _Placuna placenta_, from the eastern shores of
Ceylon.
In 1904 it was again found possible to hold a fishery in Ceylon. It was
held at a place called Marichikaddi, also on the north-west coast. In
the course of thirty-eight days over 41,000,000 oysters were taken. The
trade was very brisk; the prices paid were unprecedented. The 1905
fishery, which began on February 18, promised to beat all records. On
February 22 the catch was nearly 4,500,000 oysters; and the Government’s
share for that day was £9,000. Since this date each year has yielded a
bountiful harvest, and in financial circles the London Syndicate, who
have obtained a ‘concession’ of the oyster-beds for twenty years from
the Ceylon Government, are understood to be ‘doing very well.’
It is perhaps too soon to attribute this success to the efforts of
Professor Herdman and Mr. Hornell, the latter of whom, we understand,
has been permanently retained as biologist to the syndicate; but we have
no doubt that, acting under their advice, the oyster-bed may be made a
steady, in place of a most intermittent, source of revenue. In this
connexion it may be mentioned that radiography is now being used, and by
its means the oysters containing large pearls can be separated from
those that do not, and the latter returned to the sea. Besides their
valuable work in solving this particular problem, Professor Herdman and
his colleague have made a rich collection of marine animals, which are
being examined by a number of specialists. The results of their labours
have appeared in a handsome series of volumes published under the
auspices of the Royal Society; and it is from the first of these that
many of the facts contained in this article are derived. The memoirs
included in the volumes contain many important additions to our
knowledge; but no result is more interesting or more economically
important than the confirmation of the fact that, as M. Dubois puts it,
‘La plus belle perle n’est donc, en définitive, que le brillant
sarcophage d’un ver.’
THE DEPTHS OF THE SEA
_Here in the womb of the world--here on the tie-ribs of earth._
RUDYARD KIPLING.
The first recorded attempt to sound the depths of the ocean was made
early in the year 1521, in the South Pacific, by Ferdinand Magellan. He
had traversed the dangerous straits destined to bear his name during the
previous November, and emerged on the 28th of that month into the open
ocean. For three months he sailed across the Pacific, and in the middle
of March, 1521, came to anchor off the islands now known as the
Philippines. Here Magellan was killed in a conflict with the natives.
The records of his wonderful feat were brought to Spain during the
following year by one of his ships, the _Victoria_; and amidst the
profound sensation caused by the news of this voyage, which has been
called ‘the greatest event in the most remarkable period of the world’s
history,’ it is probable that his modest attempt to sound the ocean
failed to attract the attention it deserved. Magellan’s sounding-lines
were at most some two hundred fathoms in length, and he failed to touch
bottom; from which he ‘somewhat naïvely concluded that he had reached
the deepest part of the ocean.’
It was more than two hundred years later that the first serious study of
the bed of the sea was undertaken by the French geographer Philippe
Buache, who first introduced the use of isobathic curves in a map which
he published in 1737. His view, that the depths of the ocean are simply
prolongations of the conditions existing in the neighbouring sea-coasts,
though too wide in its generalization, has been shown to be true as
regards the sea-bottom in the immediate vicinity of Continental coasts
and islands; and undoubtedly it helped to attract attention to the
problem of what is taking place at the bottom of the sea.
Actual experiment, however, advanced but slowly. So early as the
fifteenth century, an ingenious Cardinal, one Nicolaus Cusanus
(1401-1464), had devised an apparatus consisting of two bodies, one
heavier and one lighter than water, which were so connected that when
the heavier touched the bottom the lighter was released. By calculating
the time which the latter took in ascending, attempts were made to
arrive at the depths of the sea. A century later Puehler made similar
experiments; and after another interval of a hundred years, in 1667 we
find the Englishman Robert Hooke continuing on the same lines various
bathymetric observations; but the results thus obtained were fallacious,
and the experiments added little or nothing to our knowledge of the
nature of the bottom of the ocean. In the eighteenth century Count
Marsigli attacked many of the problems of the deep sea. He collected and
sifted information which he derived from the coral-fishers; he
investigated the deposits brought up from below, and was one of the
earliest to test the temperature of the sea at different depths. In 1749
Captain Ellis found that a thermometer, lowered on separate occasions to
depths of 650 fathoms and 891 fathoms respectively, recorded, on
reaching the surface, the same temperature--namely, 53°. His thermometer
was lowered in a bucket ingeniously devised so as to open as it
descended and close as it was drawn up. The mechanism of this instrument
was invented by the Rev. Stephen Hales, D.D., of Corpus Christi
College, Cambridge, the friend of Pope, and perpetual curate at
Teddington Church. Dr. Hales was a man of many inventions, and, amongst
others, he is said to have suggested the use of the inverted cup placed
in the centre of a fruit-pie in which the juice accumulates as the pie
cools. His device of the closed bucket with two connected valves was the
forerunner of the numerous contrivances which have since been used for
bringing up sea-water from great depths.
These were amongst the first efforts made to obtain a knowledge of
deep-sea temperatures. About the same time experiments were being made
by Bouguer and others on the transparency of sea-water. It was soon
recognized that this factor varies in different seas; and an early
estimate of the depth of average sea-water sufficient to cut off all
light placed it at 656 feet. The colour of the sea and its salinity were
also receiving attention, notably at the hands of the distinguished
chemist Robert Boyle, and of the Italian, Marsigli, mentioned above. To
the latter, and to Donati, a fellow-countryman, is due the honour of
first using the dredge for purposes of scientific inquiry. They employed
the ordinary oyster-dredge of the local fishermen to obtain animals from
the bottom.
The invention of the self-registering thermometer by Cavendish, in 1757,
provided another instrument essential to the investigation of the
condition of things at great depths; and it was used in Lord Mulgrave’s
expedition to the Arctic Sea in 1773. On this voyage attempts at
deep-sea soundings were made, and a depth of 683 fathoms was registered.
During Sir James Ross’s Antarctic Expedition (1839-1843) the temperature
of the water was constantly observed to depths of 2,000 fathoms. His
uncle, Sir John Ross, had twenty years previously, on his voyage to
Baffin’s Bay, made some classical soundings. One, two miles from the
coast, reached a depth of 2,700 feet, and brought up a collection of
gravel and two living crustaceans; another, 3,900 feet in depth, yielded
pebbles, clay, some worms, crustacea, and corallines. Two other
dredgings, one at 6,000 feet, the other at 6,300 feet, also brought up
living creatures; and thus, though the results were not at first
accepted, the existence of animal life at great depths was demonstrated.
With Sir James Ross’s expedition we may be said to have reached modern
times: his most distinguished companion, Sir Joseph Hooker, is still
living. It is impossible to do more than briefly refer to the numerous
expeditions which have taken part in deep-sea exploration during our own
times. The United States of America sent out, about the time of Ross’s
Antarctic voyage, an expedition under Captain Wilkes, with Dana on board
as naturalist. Professor Edward Forbes, who ‘did more than any of his
contemporaries to advance marine zoology,’ joined the surveying ship
_Beacon_ in 1840, and made more than one hundred dredgings in the Ægean
Sea. Lovén was working in the Scandinavian waters. Mr. H. Goodsir sailed
on the _Erebus_ with Sir John Franklin’s ill-fated Polar Expedition; and
such notes of his as were recovered bear evidence of the value of the
work he did. The Norwegians, Michael Sars and his son, G. O. Sars, had
by the year 1864 increased their list of species living at a depth of
between 200 and 300 fathoms, from nineteen to ninety-two. Much good work
was done by the United States navy and by surveying ships under the
auspices of Bache, Bailey, Maury, and de Pourtalès. The Austrian frigate
_Novara_, with a full scientific staff, circumnavigated the world in
1857-1859. In 1868 the Admiralty placed the surveying ship _Lightning_
at the disposal of Professor Wyville Thomson and Dr. W. B. Carpenter
for a six weeks’ dredging trip in the North Atlantic; and in the
following year the _Porcupine_, by permission of the Admiralty, made
three trips under the guidance of Dr. W. B. Carpenter and Mr. Gwyn
Jeffreys.
Towards the end of 1872 H.M.S. _Challenger_ left England to spend the
following three years and a half in traversing all the waters of the
globe. This was the most completely equipped expedition which has left
any land for the investigation of the sea, and its results were
correspondingly rich. They have been worked out by naturalists of all
nations, and form the most complete record of the fauna and flora, and
of the physical and chemical conditions of the deep, which has yet been
published. It is from Sir John Murray’s summary of the results of the
voyage that many of these facts are taken. Since the return of the
_Challenger_ there have been many expeditions from various lands, but
none so complete in its conception or its execution as the British
Expedition of 1872-1875. The U.S.S. _Blake_, under the direction of A.
Agassiz, has explored the Caribbean Sea; and the _Albatross_, of the
same navy, has sounded the Western Atlantic. Numerous observations made
by the German ships _Gazelle_ and _Drache_, and Plankton Expedition, the
Norwegian North Atlantic Expedition, the Italian ship _Washington_, the
French ships _Travailleur_ and _Talisman_, the Prince of Monaco’s
yachts, _Hirondelle_ and _Princesse Alice_, under his own direction, the
Austrian ‘Pola’ Expedition, the Russian investigations in the Black Sea,
and lastly, by the ships of our own navy, have, during the last
five-and-twenty years, enormously increased our knowledge of the seas
and of all that in them is. This knowledge is still being added to. At
the present time the collections of the German ship _Valdivia_ and of
the Dutch _Siboga_ Expedition are being worked out, and are impatiently
awaited by zoologists and geographers of every country. The _Discovery_
and the _Gauss_, although primarily fitted for ice-work, have added much
to what is known of the sea-bottom of the Antarctic; and amongst men of
science there is no abatement of interest and curiosity as to that
_terra incognita_.
Before we attempt to describe the conditions which prevail at great
depths of the ocean, a few words should be said as to the part played by
cable-laying in the investigation of the subaqueous crust of the earth.
This part, though undoubtedly important, is sometimes exaggerated; and
we have seen how large an array of facts has been accumulated by
expeditions made mainly in the interest of pure science. The laying of
the Atlantic cable was preceded, in 1856, by a careful survey of a
submerged plateau, extending from the British Isles to Newfoundland, by
Lieutenant Berryman of the _Arctic_. He brought back samples of the
bottom from thirty-four stations between Valentia and St. John’s. In the
following year Captain Pullen, of H.M.S. _Cyclops_, surveyed a parallel
line slightly to the north. His specimens were examined by Huxley, and
from them he derived the _Bathybius_, a primeval slime which was thought
to occur widely spread over the sea-bottom. The interest in this
‘Urschleim’ has, however, become merely historic, since John Y.
Buchanan, of the _Challenger_, showed that it is only a gelatinous form
of sulphate of lime thrown down from the sea-water by the alcohol used
in preserving the organisms found in the deep-sea deposits.
The important generalizations of Dr. Wallich, who was on board H.M.S.
_Bulldog_, which, in 1860, again traversed the Atlantic to survey a
route for the cable, largely helped to elucidate the problems of the
deep. He noticed that no _algæ_ live at a depth greater than 200
fathoms; he collected animals from great depths, and showed that they
utilize in many ways organisms which fall down from the surface of the
water; he noted that the conditions are such that, whilst dead animals
sink from the surface to the bottom, they do not rise from the bottom to
the surface; and he brought evidence forward in support of the view that
the deep-sea fauna is directly derived from shallow-water forms. In the
same year in which Wallich traversed the Atlantic, the telegraph cable
between Sardinia and Bona, on the African coast, snapped. Under the
superintendence of Fleeming Jenkin, some forty miles of the cable, part
of it from a depth of 1,200 fathoms, was recovered. Numerous animals,
sponges, corals, polyzoa, molluscs, and worms were brought to the
surface, adhering to the cable. These were examined and reported upon by
Professor Allman, and subsequently by Professor A. Milne Edwards; and,
as the former reports, we ‘must therefore regard this observation of Mr.
Fleeming Jenkin as having afforded the first absolute proof of the
existence of highly organized animals living at a depth of upwards of
1,000 fathoms.’ The investigation of the animals thus brought to the
surface revealed another fact of great interest, namely, that some of
the specimens were identical with forms hitherto known only as fossils.
It was thus demonstrated that species hitherto regarded as extinct are
still living at great depths of the ocean.