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STUDIES ON!PEARL-OYSTERS | AND PEARLS.—I.
‘The Structure of the Shell and Pearls of the
Ceylon Pearl-Oyster (Margaritifera vulgaris
Schumacher): with an Examination of the Cestode
Theory of Pearl-Production. By H. LYSTER
JAMESONY M.A., D.Sc., Ph.D., F.Z.8.
tH if
[rom the PROCEEDINGS OF THE ZooLoGicaL Socrery or Lonpon,
1912.]
[Published June 1912.]
260 DR. H. LYSTER JAMESON ON
[ From the PROCEEDINGS OF THE ZOOLOGICAL Soctery OF Lon pon,
1912.)
| Published June 1912. :
Studies on Pearl-Oysters and Pearls.—I. The Structure
of the Shell and Pearls of the C eylon Pearl-Oyster
(Margaritifera vulgaris Schumacher): with an Exami-
nation of the Cestode Theory of Pearl-Production. By
H. Lysrer Jamuson, M.A., D.Sc., Ph.D., F.Z.S.
(Plates XX XTIT-XLVII. and ‘Text-figures 33-41.)
CONTEN'S. Page
(1) Introduction ......... BES rh academe eC 260
& Outline of the recent ies iceations m ( neyo Seo cide TUBERCLE eee aca 4 mee)
(3) Professor Herdman’s Conclusions on Pearl-Pormation ..................... 268
(4) Examination of the Cestode Theory of Pearl-Produetion —....... 271
(5) Description of the two Globular Cestode Larve from the Ceylon Poa
Oystererre 290
(6) Opsetounens on the Seane ture ee the TabEOue (Coy jieeisunlhae the
Cestode Larve: in Margaritifera vulgaris ....2.22...200c02-sereceerssee., 298
(7) Materials available for the Present Investigations ........0.....0..........2, 294
(8)) Methods” 2. --5.-..- ER AER SRS MRE wines a)” WAS?)
(9) Structure of the hell cuberanees Feniadiat ete sie doe Caat ERC ERE A ee ne eee OO
aes HW LherShellesecretame wl pitiheliay eee ss eceecnesceerercae ere nee eee eee meme Od
(11) Shell-Secretion So ca tatteacceneatie aloe
(12) Abnormal and Pathologic al Pinsee) a ale Shell- Sobetanee Tkcaest ee OL
(3), Viarretres: of CevlonsRearlsscc ete seatess reat c incceemececenes ota een eee Somme,
AV Miuscle=Pearl'S|t possccottnccs pcr once: ence neon eee eee TT
B. Parenchyma-Pearls (“ Cyst-Pearls,’” Herdiman) .................. 330
(14) Descriptions of the Centres of Individual Pearls .............................. Bol
ACS Materraleimomuthe bersvanuGilis asda poeet ete eek aes eee ai
B. Pearls purchased in Ceylon ............ = See cneraterenteas “Os
©. Professor Herdman’s Slides........... Aactaenana doe. stereo!
ID. Unlabelled Pearls (dry) in the British Maseant= eee BET
K. Collection of Pearls given to me by Mr. Max May (ee eer: 338
Kk. Collection of Ceylon Pearls given to me by Mr. E.
lop kins yeeeeeeeeee . 339
G. Pearls from Margar befor al Nealon is om ibe Gulf bf ikea 341
H. Pearls from WM. vulgaris trom the Mediterranean ............... 348
I. Pearls from M. vulgaris from New Caledonia .................. 843
J. Pearl from M. vulgaris from Nossi-Ré, Madagascar on 344.
K. Pearls from the Lapi shell (1/7. a ie from the edhe md
Islands, Papua ........ : 344,
~L. Pearls trom Placuna placenta ore Take Tampalakin umam,
Ceylonmeer Sees B45
M. Pearls from M. as tn var. eumingit esyer aha
Black-edged Mother-of-Pearl] pans from Seana Gam-
bier Archipelago ......... 346
(25) SGeneral Summary eects cde se See eee neti els staat ee]
(16) Works referred! Goer create ie ston ac te cena seme enectiec acl eetciye, occa eE eee mms L
(17) Explanation of the: Platestgteyesce.cceen tne re eee teen coer olccerentnaee se pee ee mmO DE
(1) Inrropuction,.
The studies which are embodied in this paper have been deferred
and interrupted. When Professor Herdman published his Report
[2
THE CEYLON PEARL-OYSTER. 261
on the Pearl-Oyster fisheries of the Gulf of Manaar (16) I was in
South Africa, and material for the examination of some of his
conclusions, which I was unable to harmonise with my own
observations made prior te my departure from England, was not
available,
Since my return I have made use of all available material
which is somewhat scanty ; and while it is insufficient to enable
me to propound, at the present moment, a working hypothesis as
to the true cause or causes of the formation of Ceylon pearls,
I think I have been able to show that the Cestode theory
enunciated by Herdman, which has formed the basis of the
somewhat meagre experiments which have been prosecuted in
Ceylon since his return to England, and which even seems to my, , ,
have led to definite regulations elsewhere*, rests on quite iAiFigion of 7
insufficient evidence, and that, if the problem of the cause of Secon}
Pearl-Production in Margaritifera vulgaris is to be solved, and a.
scheme for increasing the productivity of the Oysters evolved, a
fresh start will have to be made.
The work that still remains to be done will centre around the
causes which lead to the development of the epidermal saes in which
all pearls are formed—fine pearls and seed-pearls, “‘ muscle ”-pearls
and ‘“eyst”-pearls (or, as | prefer to call them, “parenchyma’”’-
pearls), and the mechanism which controls the secretion ot
conchyolin and the deposition therein of carbonate of lime. In
fact, I ain led back to the principles enunciated by me in 1902
(25), that the essential element in pearl-formation is the pearl-sac,
aud not the nucleus, and that it is by a study of the causes which
lead to the development of the former that the problem of the
origin of pearls is to be solved.
Some material for these further investigations has just reached
me as I] write this introduction, and more 1s promised, but, owing
to the difficulties and delays which may occur, 1 now publish
my researches on the structure of the shell, and of pearls and their
pseudo-nuclei and nuclei, without attempting to deal with the
origin of the pearl-sac.
I take this opportunity of expressing my thanks to the Ceylon
Company of Pearl Fishers, Ltd., for purchasing, ou my behalf,
pearls in Colombo to be used in these investigations ; to Professor
Raphael Dubois, for pearls from JMagaritifera vulgaris from the
Mediterranean; to Prof. W. R. Dunstan, F.R.S., for allowing me
to make use of material in the Lnperial Institute; to Mr. J.
Calcott Gaskin, Assistant Political Agent at Bahrein, Persian
Gulf, for sending me, in 1903, a number of preserved specimens
of the Lingah shell (.W/. vulgaris), some of which contained pearls ;
,
Ass
* Rules for Lower Burma under the Burma Fisheries Act, 1905. Rules 64 and 67,
which prohibited the capture of Balistes and Trygon inthe Pearl Fishery districts,
and required them, if accidentally caught, to be returned to the sea, appear to have
heen inspired by the Cestode theory. ‘These rules were cancelled in 1909. It may
be remarked that the Pearl-Oyster of Burma (the Mergui shell of commerce) is not
the same species as the Ceylon Pearl-Oyster, WZ. vulgaris Schumacher, but is the
ereat Mother-of-Pearl Oyster, IZ. maxima Jameson.
re
[3]
bo
62 DR. H. LYSTER JAMESON ON
to Mr. E. Hopkins, of Hatton Garden, for specimens of Ceylon
Pearls; to Professor W. A. Herdman, F.R.S8., for specimens of
Pearl-Oysters from Ceylon, and for allowing me to examine his
preparations ; to Mr. Max Mayer, of Hatton Garden, for specimens
of pearls for my work; to H.H. the Jam Saheb of Nawanagar,
for specimens of Pearl-Oysters from the Gulf of Kutch ; to Prof.
L. G. Seurat, for pearls from New Caledonia, Madagascar, and the
Gambier Archipelago; to Mr. A. E. Shipley, F.R.S., for allowing
me to examine and make use of his specimens of J'ylocephala and
allied genera of Cestodes from Ceylon fishes; to Mr. E. A. Smith,
1.8.0., for permitting me to make use of material in the British
Museum (Natural History), including specimens from Dr. Kelaart’s
collection; and to Mr. A. Van Noorden (of the firm M. Myers,
Mother-of-Pearl Merchants) for specimens of Lingah and other
shells.
After this paper was handed in I received a copy of Rubbel’s
paper (34a) setting forth in greater detail the results already
published by him (33 and 34). Herr Rubbel and I have arrived,
working independently on widely different molluses, at identical
conclusions on several important points, such as the nature of
Herdman’s ‘“calcospherules.” Where practicable, I have inter-
polated references to his work in the text, and my only regret is
that it is not possible to discuss his valuable work more fully in
the present paper and to dwell at length on the many points where,
adopting a slightly different terminology and interpretation of the
phenomena, our respective works lead to the same conclusions.
(2) OUTLINE OF THE RECENT INVESTIGATIONS IN CEYLON.
In January 1902 Professor W. A. Herdman went to Ceylon, at
the request of the Colonial Office (who availed themselves of his
services on the recommendations of the Council of the Royal
Society and of Professor Ray Lankester), to investigate the
condition of the Pearl-Banks. Professor Herdman took with him
as his assistant Mr. James Hornell, who remained in Ceylon to
carry on the work after the former’s return to England in April
of the same year, and who collaborated in the preparation of
Professor Herdman’s reports. Professor Herdman’s visit in 1902
gave him seventy-eight days in Ceylon, and was largely spent in
an extensive biological and faunistic survey of the pearl-banks,
carried out on two successive dredging-cruises, each of several
weeks’ duration ; and he credits Mr. Hornell with the major part
of the observations on Pearl-production (Royal Institution
Lecture of March 27th, 1903) (14). Prof. Herdman himself
always seems to have regarded the condition and welfare of the
natural beds of oysters as a more important problem than the
question of pearl-production (Report on the Ceylon Pearl
Fisheries, Part I. p. 5, and Part V. p. 29; also Report of the
Annual Meeting of the Ceylon Company of Pearl Fishers, Ltd.,
[4]
THE CEYLON PEARL-OYSTER. 263
for 1908*). In fact, he contends on p. 30 of Part V. of his Report,
and in his address to the Linnean Society on 24th May, 1906,
that
“to reverse the popular saying, if we attend to the prosperity
of the bed as a whole, the individual oysters may be left to
take care of themselves, both in regard to health and pearl-
production.”
In January 1904 Mr. Hornell was appointed Marine Biologist
to the Government, to which post were subsequently added the
administrative duties of Inspector of Pearl-Banks. While holding
these Government appointments Mr. Hornell continued to colla-
borate with Prof. Herdman, though it is clear that the executive
and administrative duties attached to his post interfered not a
little with the more strictly scientific observations. Thus, in his
Report on the Inspection of the Ceylon Pearl-Banks, November
1905, Mr. Hornell says (23), p. 6 :—
“The working out of this material must of necessity await
the long deferred time when a pause shall occur in the
field work in which I have been engaged for the past
eighteen months, and which permits me no leisure for the
correlation and marshalling of biological data.”
And, again, in Reports from the Ceylon Marine Biological
Laboratory, No. 1, p. 23, 1905, he says :—
“The Marine Biologist should be given opportunity to
further investigate the life of the spherical Cestode so abun-
dant in the Pearl-Oyster, and which is the inducing agency
in the formation of ‘cyst-pearls’ (‘fine pearls’). The
problem is far from solution, and will entail much unpleasant
and trying labour before a satisfactory conclusion can be
hoped for.”
The observations of Prof. Herdman and Mr. Hornell on the
spot were corrected and correlated by laboratory work in Liverpool,
carried out by Prof. Herdman and his staff at the University, on
the material sent home for investigation. Prof. Herdman has
courteously allowed me to examine the slides made during these
investigations, showing sections of Pearls in situ in the tissues,
and of the Cestode larvee which he asociates with pearl-formation.
In March 1906 the Ceylon Company of Pearl Fishers, Ltd., was
formed and the pearl-fisheries were leased to the Company by the
Government, at a yearly rental of Rs. 310,000, the lease carrying
the obligation to spend, in addition to the above rent, a sum of
from Rs. 50,000 to Rs. 150,000 yearly ‘on the experimental or
* Financial Times, Dec. 19,1908. Sir West Ridgeway, Chairman of the Company,
on this occasion said that
“with regard to biological research, Prof. Herdman was of opinion that in
the present condition of the Company’s pearl-banks accurate navigation,
careful and exhaustive inspection of the ground, and wise administration are
more important than the purely scientific side of the business.” :
[5]
264 DR. H, LYSTER JAMESON ON
practical culture of the pearl-oyster and on the improvement of
the pearl-banks ” (50).
On the formation of the Company Mr. Hornell was transferred
to its service as local General Manager, Prof. Herdman being
made Scientific Adviser.
In April 1908 Prof. Herdman, at the request of the Company,
paid another short visit to Ceylon, to enquire into the question of
the inspection of the banks and other branches of the business.
As a result of Prof. Herdman’s inquiries, the post of General
Manager was abolished, being merged in that of Managing
Director, and Mr, Hornell resigned, being succeeded by Mr. T.
Southwell, A.R.C.Se. (Lond.), who since 1907 had been acting as
Mr. Hornell’s assistant, and previously to that had assisted
Prof. Herdman in his laboratory at Liverpool in the preparation
of the material sent home for investigation. Mr. Southwell
was made Scientific Adviser, a post which he still holds. Pro-
fessor Herdman continued to be retained in an advisory capacity.
Capt. J. Kerkham was appointed Superintendent of Fisheries*.
Besides the work of the Company’s scientific employees, Dr. A.
Willey, in his capacity as Marine Biologist to the Government
(a post which he held along with the Directorship of the Ceylon
Museum), has published some observations in the Ceylon
Administrative reports and in ‘ Spolia Zeylanica.’
Particuiars of the work done, and of the conclusions arrived at,
by these several naturalists will be given in the course of the paper.
In considering the incompleteness of the observations, despite
the eight and a half years that have been devoted to the study of
the Ceylon pearl-banks and the very large sums of money that
have been expended, it must, of course, be borne in mind that for
the last three or four years the banks are stated to have been
practically bare of oysters t+, and the prosecution of the investi-
gations initiated by Prof. Herdman has thus been seriously
hampered. But it is amazing that a Company whose prospects
were so largely dependent on scientific work should have failed
to set by an adequate stock of properly preserved material for
scientific Investigations and to establish at a suitable station a
reserve of live oysters when the oysters were passing through
their hands by the million. Had this been done, the barren
years that have now come might have been devoted to the
examination and amplification of Prof. Herdman’s observations,
* Since the above was written the operatious of the Company have ceased. Tt was
announced in the ‘Times’ of April 4th, 1912, that the lease had been terminated,
a deposit of £10,000 together with the property of the Company being forfeited to
the Government. An examination of the causes of the failure of this short-lived
Company, which started with a capital of £165,000, has lately been published by the
present writer (26 a).
+ Not entirely ; for it was possible to obtain 12,000 oysters in Feb. 1910 for Mr.
Southwell’s feeding experiment described in Part V. of the Ceylon Marine Biolopieal
Reports, p. 213, and no less than 35,000 oysters ranging from 8 months to 24 years
old were obtained for the experiment described in Part Iv. of the same publication,
p. 169. Mr. Southwell, in a paper published in May 1911 (42), s says: “ The only bed
which now exists is confined to an inshore area, and the oysters found thereon only
rarely contain the pearl-inducing parasite.”
6]
THE CEYLON PEARL-OYSTER. 265
which of necessity were somewhat cursory and superficial. The
result of this lack of foresight has been that the energy that ought
to have been concentrated on an intensive study of the pearl-
oyster and the mechanism of pearl-formation appears to have
been largely dissipated on general faunistic work, such as the
description of new species of crabs and tapeworms, matters which,
valuable as they are from the purely scientific standpoint, have
only a secondary bearing on the problem of increasing and
rendering more reliable the supply of pearl-oysters and pearls.
(3) Proresson Herpman’s Conciustons on Peart-ForMmarion,
Professor Herdman distinguishes several causes of pearl-
formation, though only two of these are regarded as of sufficient
frequency to have economic importance, viz. Cestodes, causing the
majority of “cyst-pearls,” and “ caleospherules,” causing “muscle-
pearls.” I will pass over the pearly excrescences or ‘blisters ” on
the inside of the shell, due to the irritation of boring animals or
intruding particles of foreign matter, as these should be kept in
a category entirely distinct from true pearls. The latter term,
following my paper published in 1902 (25), I shall confine strictly
to bodies developed independently of the shell, which are not in
any way continuous with the shell, except where, owing to the
rupture or absorption of the intervening tissues, they may become
secondarily covered over with nacre continuous with the lining of
the shell. When this happens to a pearl it becomes an “attached
pearl,” a body quite other than a blister. Attached pearls are
valued for the true pearl that can often be dissected out of them,
whereas blisters are used as substitutes for pearls where the
imperfect side can be concealed in the setting, e. gy. in cheap
jewellery, rings, pins, brooches, etc. Prof. Herdman (Report I.
p- 10) apparently applies the name ‘“‘ ampullar pearls ” to blisters,
that is to say to bodies “which are not formed within closed
epithelial sacs like the others, but lie in pockets or ampulle of the
epidermis,” and on p. 146 of the same part speaks of blisters as
‘pearls of an inferior quality,” but I cannot help feeling that, in
scientific terminology at least, it is undesirable to apply the term
‘pearl ” to these bodies at all.
Professor Herdman recognises the following causes of pearl-
formation in the Ceylon pearl-oyster :—
(i) Grains of Sand and other Foreign Particles.
These, in the experience of Professor Herdman and Mr. Hornell,
only form the nuclei of pearls under exceptional circumstances.
In the whole of their observations they have only records of three
such cases out of hundreds of pearls examined (Report V. pp. 4
& 127). They say (V. p. 28) :—
‘* Probably it is only when the shell is injured, e. g., by the
breaking of the ‘ears,’ thus enabling sand to get into the
interior, that such particles supply the irritation that gives
[7]
266 DR. H. LYSTER JAMESON ON
rise to pearl-formation. The ectoderm, in such cases,
would probably also be damaged, and cells may be carried in
with the inorganic particles.”
As shown below, the presence of grains of sand and other foreign
particles in the nuclei of some Ceylon pearls has been confirmed
by the present writer.
(i1.) Boring Animals.
While recognising that pearly exerescences or “ blisters ” are
mainly due to borers such as Lewcodore and Clione, Herdman and
Hornell say (Report V. p. 28) that
‘in exceptional cases a free pearl may be formed in this
way.”
No specific instances, however, are cited, nor is any explanation
suggested as to what would be the mechanism in such cases.
(iil.) Parasites other than Cestodes.
In his lecture at the Royal Institution, referred to above,
Prof. Herdman said:
“We shall I think be able to show in our final report that
Cestodes, Trematodes and Nematodes are all concerned in
’ : .
pearl-formation.”’
At the same time he recognised the “ larval Cestode of the
Tetrarhynchus form” as the most important cause. Again, in the
Y LY tohite)
Report (V. p. 29), Herdman and Hornell say :
‘A fuller experience is causing us to incline to the view
that various parasites may act as pearl nuclei, even in the same
molluse. Some pearls are certainly formed around intrusive
Nematodes. We have a complete cyst pearl, free and
unattached, of which the nucleus is a coiled Cheiracanthus
uncinatus, on which the pearl deposit is not sufficiently thick
and opaque to obscure the coils so as to render identification
difficult.”
This pearl does not appear to be in Prof. Herdman’s collection.
(iv.) Pearls without a Nucleus.
Prof. Herdman points out that both in the case of the Ceylon
Pearl-Oyster and J/ytilus some pearls have no trace of a nucleus
(Report V. p. 18). He figures one such pearl from Mytilus,
magnified 100 times. The existence of pearls without nuclei
was recorded by Harley (11) in 1889. The observations set
out below show that in the Ceylon Pearl-Oyster, both in muscle-
pearls and in a great nuinber of parenchyma-pearls, the presence
of a nucleus of foreign origin is quite unnecessary, and point to
the conclusion that the origin of the pearl-sac is usually due to
stimulation other than that caused mechanically by such bodies.
So far as Mytilus is concerned, I attribute the conditions where
[8]
THE CEYLON PEARL-OYSTER. 267
a nucleus is absent to two alternative causes. In the first case, the
Trematode described in my paper on the Origin of Pearls in
the P. Z.8. for 1902 (25) may migrate out of the sac, in which a
pearl without any nucleus, or with a nucleus consisting of a few
residual granules, may subsequently be formed. In the second
case, in certain localities, Mytilus edulis produces pearls through
an agency (which I am at present trying to investigate) other than
Vermian. These pearls may have as nuclei either a few dark
granules or nothing that can be detected without the use of much
higher magnification than 100 diameters. One of them is shown
at C in text-figure 33 (p. 277).
(v.) Musele-Pearls.
The discovery of “‘muscle-pearls” was, I believe, first announced
at the British Association Meeting in September 1903.
Under this name (Brit. Assoc. Report, Southport, 1903, p. 695)
Prof. Herdman distinguishes pearls formed “around minute
calcareous concretions, the ‘ calcospherules, which are produced
in the tissues and form centres of irritation.” They occur “ most
abundantly in the muscular tissue near the insertions of the
levator and pallial muscles.” (Report, Part V. p. 27.) Herdman
and Hornell say, speaking of muscle-pearls :
“at seems probable that these have been formed by the
deposition of calcareous matter around a minute calculus in
the tissues”.... ‘The Muscle pearls when present are
usually abundant, and when examining under the microscope
a young pearl of this kind, im sitw, it is common to find a
large number of minute calcareous depositions or calco-
spherules scattered in the neighbouring tissue. It is probable
that the muscle pearls are formed around these microscopic
calcospherules as centres of irritation, and as these [? the1 |
positions are invariably in our experience close to the surface
of the muscle or the mantle, there is no difficulty in under-
standing that there, if anywhere, ectoderm cells might
migrate to the source of irritation and thus be responsible
for the deposition of a pearl.” (Report V. p. 27.)
Muscle-pearls are especially numerous in certain localities ;
Prof. Herdman instances (Report V. pp. 30-31) that they were
particularly numerous on the 8.E. Cheval Paar in 1902 and 19038,
and
“that the vigorous and healthy oysters of the Eastern Cheval
and Periya Paar Karai produce practically all the examples of
this class of pearls,”
the numbers produced on other banks being insignificant.
Mr. Hornell, speaking of an examination of a number of pearls
attached to the shell, states that ‘ decalcification of the pearls
attached to muscle-scars reveals no organic nuclei, whereas the
jattached] pearls irregularly disposed have Cestode embryos as
nuclei, exactly as ‘fine’ pearls have.” (19, p. 12.)
[9]
268 DR. Hl. LYSTER JAMESON ON
Mr. Southwell (40, p. 194), referring to the caleospherules
causing “ muscle-pearls,” says :
“The origin of the latter bodies is quite unknown,
although it seems almost certain that they are depositions
from the blood.”
Again, in a later paper (42, p. 128), Mr. Southwell says :
“ Other pearls are also found in the Oyster, but they have
no organic nucleus. Such pearls are termed muscle or seed
pearls. ‘Their origin is obscure, but they are always found
near the muscle insertions, and are believed to be formed
round a calcospherule of excretory origin, or by the sheer of
muscles moving in different planes.”
In the first mentioned of the above papers (40), he goes on to
say:
“Considerably more pearls are formed round calcospherules
than round parasites, the ratio being about 13 to 1. They
are therefore of considerable commercial importance.”
Unfortunately, Mr. Southwell does not give the number or
sources of the pearls on which this statement is based, although
if is quite clear, from the observations of Prof. Herdman and
Mr. Hornell, that ‘‘ muscle-pearls ” are characteristic of certain
localities, and “ cyst-pearls ” of others, and that the ratio may vary
greatly on different banks.
My own observations on ‘* Muscle-pearls” and on the nature of
the so-called “ caleospherules” are given in a later part of this
paper.
(vi.) Cestode Larve.
Of fine or “ Orient” pearls Prof. Herdman and Mr. Hornell
claimed that the most frequent nucleus is a Cestode larva. In
their ‘ Conclusions on Pearl-Formation ” (Report V. p. 29) they
maintain that their investigations have shown * that in J/argariti-
fera vulgaris, at Ceylon, the production of the *‘ Orient’ pearl is
dependent upon Cestode infection and that the species mainly
concerned is Tetrarhynchus unionifactor,” and in the General
Summary of their Ceylon Report (V. p. 127) they say :
“The majority of these fine pearls contain as their nuclei
the more or less easily recognisable remains of certain
Platyhelminthian parasites, which we identify as the larval
condition of Cestodes belonging to the genus Vetrarhynchus.”
It is stated several times that this supposed identification was
made during Professor Herdman’s second cruise in March 1902,
but its elaboration must have been, in great part, the work ot
Mr. Hornell at a later date. The narrative of the Cruise
(Report I. p. 70), published in 19038, states, in a paragraph
apparently inserted between the records of March 6th and 7th:
“In the intervals of dredging and when moving from
place to place, we were now continuously engaged in
[10]
THE CEYLON PEARL-OYSTER, 269
examining the parasites of the pearl-oyster and their
influence on pearl-formation. We also decalcified such pearls
as were found. ‘This work was continued as time permitted
during the next few weeks, and also by Mr. Hornell after I
left. We found various parasites, in the liver especially,
some of which were Platyhelminthian and others Sporozoan
in their nature, and some of which were enclosed in
calcareous capsules. Mr. Horneil afterwards determined
that these were Tetrarhynchus larve of Cestodes, and we have
no doubt that they are in many cases the nucleus of the
pearl, and the irritating cause of its formation.”
Again, in the preface to Part IL. of his Report, p. vi, dated July
1904, Prof. Herdman says :
* On the Cheval Paar, in March 1902, we satisfied ourselves
that the ‘Orient’ pearl, free in the tissues of the pearl-
oyster, is deposited around a cyst containing a Cestode larva,
and preliminar y notices to this effect were published in my
Royal Institution Lecture of March 27, 1903, and at the
Southport Meeting of the British Association in September
LOS?
On p. 6 of Part V. of the Report (Pearl-Production), Herdinan
and Hornell say :
“One of the first facts that we were able to determine
in connection with the Ceylon Pearl-Oyster, in the spring of
1902, was that the Orient pearl in the Gulf of Manaar is
deposited around the young larva of a Cestode.”
And on p. 15:
“ We found the Cestode larvee in association with pearls in
the tissues during our cruises in the ‘ Lady Havelock’ in the
Gulf of Manaar, in February and March, 1902. It was about
March 6th (see ieee! p. 70,in Part Tg when cutting up
Oysters from the western part of the Cheval Paar, that we
first became convinced that the opaque white elobul: ar larvee
we were finding encysted in the liver belonged to Cestode
worms.”
On the other hand, Shipley and Hornell, in their paper on the
Parasites of the Pearl-Oyster (Herdman’s Report, IT.), seem to
imply that at least the elaboration of these observations was
carried out subsequently to Professor Herdman’s departure from
Ceylon. Thus, they say (p. 79):
“These larvee first attracted attention during the second
cruise of the ‘ Lady Havelock.’ on March 6th, 1902, when
numbers of the early globular stage were dissected out from
the livers of oysters dredged from the West Cheval Paar.
Subsequently, during the investigation carried out at the
Galle Biological Laboratory, a second and more advanced
‘yy S
stage of a Tetrarhynchus larva was found in the same
[11]
270 DR. H. LYSTER JAMESON ON
material. Details of the morphology and histology were
then worked out, and the relationship which the larve bear
to pearl-formation was investigated.”
Strange to say, Professor Herdman’s Preliminary Report to
the Government, dated July Ist, 1902 (18), makes absolutely no
reference to the discovery in the previous March of this important
aspect of the parasites of the Pearl-Oyster.
In the Preliminary Report referred to, Prof. Herdman says
(p. 2):
‘Samples of all the oysters obtained by us were examined
for parasites and for any diseases or abnormal conditions, and
although a considerable number of minute parasites, both
Protozoan and Vermean, were found, still that is by no
means unusual amongst molluscs, and we do not consider
that we saw anything which gave evidence of any epidemic
disease or widespread and injurious prevalence of parasites.”
And again in the same Report (p. 4), in his summary of
conclusions, the Professor says :
“A considerable number of parasites, both external and
internal, both Protozoan and Vermean, were met with, but
that is not unusual in molluses, and we do not regard tt as
affecting seriously the oyster population.” (‘The italics are
mine.)
Tn view of the last three quotations, if it were not for the very
definite assertions in Part IT. p. vi, and Part V. p. 6, of Professor
Herdman’s full report, quoted above, I should be almost inclined
to think that, while the Cestode larvee were no doubt discovered
“in association with pearls” during Professor Herdman’s cruise,
the Cestode theory of Pearl-formation might have been evolved
after Professor Herdman’s return to England, and after the above-
mentioned preliminary report had been submitted. In that case
Mr. Hornell might well have been misled by the false analogy of
the case of the Trematode origin of pearls in A/ytilus, which was
dealt with at length in my paper (25). This paper appeared
in August 1902; that is to say shortly after the Professor’s pre-
liminary report of July Ist, 1902, containing no reference to the
Cestode theory, was submitted. The view that my paper might
have misled Mr. Hornell and Professor Herdman would also derive
support from the fact that the real point of my paper had apparently
been missed, viz. that it is not the presence of any parasite, but
the specific stimulation of a narticular kind of parasite that
causes the growth of the pearl-sac. I consider this point is by far
the most important contribution I have so far made to the subject,
and I believe it will be the basis upon which a rational system of
artificial pearl-production will ultimately be built.
The first announcement of Prof. Herdman’s theory of Pearl-
formation seems to have been made at a lecture delivered before
the Royal Institution on March 27th, 1903, an abstract of which
appeared in ‘ Nature’ for April 30th of the same year (14).
[12
THE CEYLON PEARL-OYSTER, ial.
(4) EXAMINATION OF THE CESTODE THEORY OF PEARL-PRODUCTION.
It is unfortunate that more figures of pearls containing as nuclei
supposed Cestodes are not given in Prof. Herdman’s account of
Pearl-formation, The only figures that represent the nuclei of
decalcified pearls examined entire * as transparent objects appear
to be those on plate ii. in the Section on Pearl-Production in
Part V. of the Report, figures 5 and 7, figure 6 representing a
dead Cestode in a partially calcified cyst (not, however, a pearl).
On p. 22 it is stated that these drawings, which are reproduced
from Shipley and Hornell’s article upon the parasites of the Pearl-
Oyster in Part II. of the Report, are the work of Mr. Hornell,
and it is not evident from the text that Prof. Herdman had ever
seen the specimens from which they were made. Turning to these
same figures on plate i. of the article by Shipley and Hornell on
the parasites of the Pearl-Oyster (Part I]. of the Report, figs. 5
(A) and 8 (B), (C), (D)), we find them described in the Explana-
tion of the Plates as the nuclei of decalcified pearls; but the same
figures are referred to in the text, p. 80, as representing the
Cestode larva enveloped in its “tough elastic and fibrous capsule
of spherical form, derived from the adjacent connective tissue
cells.”
It is, I think, hazardous to identify these figures as the remains
of Cestode larve without examination of sections, and I eannot
help feeling that each of these figures is capable of comparison
with the non-Cestodian centres of pearls described by me below.
Tt is a remarkable fact that nowhere throughout the Report is
there figured a section of a decalcified pear] showing the Cestode
remains in the nucleus, and to this fact I may fale my own
observation that of all the pearls sectioned in situ by Prof. Herd-
man, numbering about 25 (not counting some minute clustered
muscle-pearls), which he kindly sent me to examine, I could not
find a single nucleus that I was able to accept as being a Cestode
or other Vermian parasite. The characters of the nuclei in these
preparations are described in the part of the paper which deals
with my own researches.
The superficial resemblance of the pearl figured on plate ii.
fig. 4.4, im Part II. eo) of the Report, anda gain in Part V.
(Pear]- Production), pl. i. fig. 5 &, c, d, & e, to the globular Cestode
Jarve found in the Oyster is hardly enough to go upon. If such
a pearl consisted of a parasite thinly coated with nacre if would
probably be dark and valueless and not a “fine pearl,” for the
yellowish-brown dead tissue of the Cestode should be clearly
visible through the nacreous coat. It is not stated whether this
pearl was decalcified and sectioned to test whether the resemblance
was more than “ skin deep.”
* These figures are referred to by Southwell (42), p. 128, as “figures of sections
of decalcified pearls,” but they are not described as suc h in the text; and they
certainly appear to be no more than drawings of the centres of pearls examined as
transparent objects.
[13]
Die, DR. H. LYSTER JAMESON ON
With regard to the mechanism by which the Cestode is supposed
to cause pearl-formation, Prof. Herdman is unable to contribute
much. He seems to recognise that the particular conditions
necessary to transform the Cestode into a pearl-nucleus are not by
any means universally present, and that it is only, so to speak,
under exceptional circumstances that the Cestode, which is very
abundant in the Ceylon Pearl-Oyster, becomes the centre of a pearl.
The larva is surrounded by a connective-tissue cyst, and has not
been satisfactorily demonstrated in any instance with an epithelial
*‘ pearl-sac” (such as I described tor the Pearl-inducing 'Trema-
tode in Mytilus), though supposed proliferations of cells inside the
connective-tissue cyst are figured in the Report (Part V. Pearl-
Production, pl. iii. fig. 7). These, being inside a thick fibrous
connective-tissue capsule, are difficult to accept as being equivalent
to a pearl-sac, which I generally find to be surrounded by the
spongy subepidermal parenchymatous tissue, except in the case
of those parts of a ‘ muscle-pearl” into which muscle-fibres are
inserted. From my own observations I am rather inclined to
regard these “cells” as granules excreted by the parasite itself,
with possibly an admixture of wandering leucocytes. In any ease,
if this is an epithelial pearl-sac, what becomes of the thick fibrous
eyst outside it, which is certainly not present around the pearls ¢
Professor Herdman himself (see below) does not think the Cestodes
enveloped in thick connective-tissue cysts are destined to become
nuclei of pearls.
The supposed migration of ectoderm-cells into the wall of a
pearl-sac already formed and already containing a pearl, as figured
in Part V. (Pearl-Production), pl. i. figs. 18-20, seems to be a
matter quite apart from the question of the primary origin of the
pearl-sac.
On p. 23 of Part V. Prof. Herdman says :—
“Tt is quite evident from the examination of a large series
of sections, such as we have worked through, that the
inajority of these encysted parasites do not become encased
in pearls. Probably none of those in thick connective-tissue
cysts are destined to form nuclei. They are awaiting their
legitimate further development in the next host, after their
sheltering molluse has been devoured by a fish. In such
cysts and around such parasites we find no epithelial sac, and,
as a consequence, there can be no pearl. Whether or not it
is the case that only dead parasites supply the stimulus
necessary to induce pearl-formation, and whether, as Giard
has suggested, the parasites may be infested and killed by a
species of Glugea, so that that Sporozoan comes to be even-
tually responsible for the pearl, we are not prepared to say
—we have found no fresh evidence in the Ceylon material
bearing upon that point. It seems clear to us, however, that
the epithelium is always associated with pearl-formation, and
that in the absence of the epithelium only a thick-walled
connective-tissue cyst is produced. If we adopt the view (see
[14]
THE CEYLON PEARL-OYSTER. 273
below) that this epithelium is genetically related to the
ectoderm, then a possible explanation of the difference in
behaviour in the encysted condition would be that those larvee
that carried in ectodermal cells become covered (when dead or
while still alive) by a pearl-sac and embedded in a pearl,
while those that were free from ectoderm become surrounded
by the connective-tissue cyst.”
No satisfactory instance, however, is recorded of the Cestode
parasite being observed surrounded by an epidermal sac.
Again in Part III. of the Report, p. 32, Professor Herdman,
quoting a Report furnished to him by Mr. Hornell, says the
abundance or otherwise of cyst-pearls “ is connected with the
factors which control the relative abundance of the pearl-inducing
Cestode and those which conduce to its death during encystment
in suitable localities within the tissues—problems as yet obscure ” ;
while in Part V.(Pearl-Production), p. 15, he says “it is appar-
ently very difficult indeed to hit upon a stage showing the
commencement of the pearl-formation.”
And again, in an address delivered at the Anniversary Meeting
of the Linnean Society of London in 1906 (17), Prof. Herdman,
speaking of his Ceylon work, says that it is probably only those
Cestodes that are provided with an ectodermal covering forming
a pearl-sac that become the nuclei of pearls. But, as stated above,
such an ectodermal pearl-sac has not yet been found to occur
around the parasite, and its occurrence is purely theoretical.
The investigations made subsequently to the publication of
Prof. Herdman’s Reports have added little to our knowledge of
the subject. In 1905 Mr. Hornell published a Report on the
Placuna placenta pearl-fishery of Lake Tampalakamam, dated
June 15th, 1905 (21). In this he states (p. 5) that he dissolved
two Placuna pearls (out of five in his possession) and found that
“in each case the nucleus proved to be the dead remains of a
minute Platyhelminthian larva of the same stage and species as
that which forms the nucleus of cyst-pearls in Margaritifera vul-
garis.” Further study revealed the presence of Cestode larve in
the dorsal portion of the visceral mass. He considers that these
are identical in details of form and structure with those of Mar-
garitifera vulgaris, but expresses some doubt as to their specific
identity, and adds that if they prove distinct the Placuna
parasite will need afresh name. Mr. Hornell further observed
that these larve multiply asexually by a process of endogenous
budding, which he wrongly refers to as parthenogenesis.
Mr. Hornell then goes on to make the following extraordinary
statement, which I quote as giving some indication of the con-
fusion of ideas which existed as to the identity of the supposed
pearl-producing larvee even in 1905, 7. e. nearly three and a half
years after the beginning of the observations :—
“The discovery of a stage in the life-history of this
parasite, which I am confident is homologous with the
Proc. Zoou, Soc.—1912, No. XVIII. 18
274 DR. H. LYSTER JAMESON ON
Redia-stage of a Trematode, confirms my original idea of it
being a ee al Trematode—an idea formed miben first I saw
it in March 1902” |2.e. the Cestode larva in Margaritifera
vulgaris|. “ Other facts point to the same conclusion, and |
have now no doubt on the subject. The genus to which it
belongs is still doubtful, but as it is inconvenient not to have
a name whereby to make mention of it, I shall henceforth
refer to it under the cognomen of Distomum (¢) margariti-
factor, n. sp., the specific name having reference to the fact
that it is the inducing cause in the production of ‘ fine’
pearls.”
‘Mr. Hornell anticipated that asexual reproduction would be
found to occur in the Cestode parasites of Margaritifera vulgaris
also, and this has since proved to be the case.
An expurgated edition of the above report was published in
1906 (22), which, however, bore the same date, June 15, 1905, as
the Sessional Paper. In this the statements as to the supposed
Trematode nature of the parasite were suppressed (though not
formally withdrawn), the name “Distomum margaritifactor, n.sp.,”
cancelled with a stroke, still figuring in the lithographed plate
(Annexure IT.).
As explained below (p. 345) I have been unable to confirm the
presence of Cestodes in the centres of Placuna pearls from Ceylon,
any more than I can find them in the pearls of Margaritifera
vulgaris.
In 1907 Dr. A. Willey (48) confirmed and extended Mr. Hornell’s
observations on the endogenous reproduction of the Placuna
Cestode.
Mr. Southwell discovered (39, p. 173) that endogenous asexual
reproduction or budding, similar to that described by Hornell and
Willey in the parasite of Placuna occurs occasionally in the Cestode
parasites of the Pearl-Oyster. He only observed the occurrence
twice, in November 1906 and January 1909—in each case a single
endogen was found.
In 1903 the late Professor A. Giard (10) announced that
M. L. G. Seurat believed that in the black-lipped Pearl-Oyster
of the Gambier Archipelago (Margaritifera margaritifera var.
cumingii Reeve) pearl-formation was due to the presence of a
parasite, figures of which were given, and which Prof. Giard
referred to a genus near to Cyathophyllus [| Cyathocephalus ?|
Kessl. or Acr -obothr ium Olsson.
Subsequently Seurat found the adult of this worm in the
Eagle Ray (Aétobatis narinari Kuphr.) in the spiral intestine, and
named it Tylocephalum margaritifere (36). The adult, which is
figured by Seurat (37), is quite a minute worm, not exceeding
4 mm.
The scolex occurs in eysts, similar to those occurring in the
Jeylon Pearl-Oyster, and multiple cysts (perhaps for med | by bud-
ding of the larva as in the Placwna eee) occur also, Seurat
[16]
THE CEYLON PEARL-OYSTER. 2h
states that these cysts which form around the parasites become
the nuclei of pearls, and a decalcified pearl shows an organic
nucleus in the centre surrounded by concentric layers of conckyolin,
the whole having a diameter of about a millimetre, and the nucleus
being a scolex *225 mm. long and easily recognisable as that of
T'ylocephalum.
It appears that in this case also the parasites may be present
in great numbers without pearls being found (Seurat (35), 1904,
p- 295).
Here, again, examination of the scanty material available (see
p- 346) has yielded no confirmation of the presence of Cestodes in
the pearls of J. margaritifera var. cumingit. Iam endeavouring
to obtain further material from the Eastern Pacific, in order to
extend my observations on this species.
I may say that from the first time I read Professor Herdman’s
Reports and papers on the subject I was sceptical as to the
relationship of the Cestode to pearl-formation.
Indeed, before Prof. Herdman’s departure for Ceylon, on
examining Dr. Kelaart’s material at the British Museum, which
Mr. KE. A. Smith kindly placed at my disposal, I had detected the
existence of these Cestode iarvee (which Kelaart seems to have
regarded as “eggs of Entozoa”) in their connective-tissue cysts in
the Ceylon pearl-oyster, and after having examined the larvee, and
also having decalcified pearls from the same oyster, dismissed the
Cestode as probably not concerned in pearl- formation.
My chief grounds for doubting the Cestode theory were the
following :—
(a) The absence of evidence that the Cestode ever occurred in
an epidermal sac, and the fact that it was almost invariably sur-
rounded by a fibrous capsule or cyst which does not oceur around
the pearl.
(6) The large proportion of the Cestodes that showed no sign
of becoming pearl-nuclei, pointing to the conclusion that pearl-
formation does not necessarily, or even normally, follow from
infection. Thus, in a footnote to p. 12 of Part V. of his Report,
Prof. Herdman says :
“In comparing these statistics |7. e. of numbers of parasites
and of pearls in Mytilus] with those of the Ceylon pearl-
oyster, one is struck by the wholly different ratio borne
by pearls to parasites in thetwo cases. In the mussels,
pearls are far more numerous than the living parasites. In
our Ceylon oyster, parasites may be exceedingly abundant * ;
while pearls (cyst-pearls) are relatively very rare, probably
not more than one to a hundred parasites.”
* Mr. Southwell (42), p. 128, says; *‘ As many as 120 have been counted in asingle
oyster ”’; and further down on the same page: ‘‘ Occasionally several hundred oysters
can be examined, each containing 20 or 30 cysts, and not a single pearl is to be
found,”
18*
[17 |
276 DR. H. LYSTER JAMESON ON
In this connection an observation made by Dr. Willey (49)
is very significant. Dr. Willey says :-—
“« A remarkable fact, indicating the subtle dependence of
the pearl-producing molluscs upon their environment, is that
whereas the most ‘valuable pearls, called cyst-pearls by Prof.
Herdman, are formed about a parasite as their centre or
nucleus, yet the presence of these parasites in great numbers
does not necessarily predetermine the formation of pearls.
Pearl-oysters at Trincomalee may be heavily infected with
the parasites without yielding pearls. It may be said that
the parasitic infection and the pearl-disease are two separate
phenomena, the latter proceeding from the former under
certain conditions which are realised in the Gulf of Manaar.
Whether these exact conditions can be reproduced elsewhere
is one of the main problems before the Company. In the
same way the cultivation of the oysters and the multipli-
cation of pearls are two separate operations, the latter
proceeding from the former in response to cer tain conditions
affording the suitable stimulus. Conditions may favour the
bivalves, but not their parasites; or they may favour both
hosts and parasites, but not the production of pearls.”
(c) Professor Herdman’s statement on p. 17 of Part V. of his
Report that Mytilus pearls (which he examined in order to be
able to correlate his work with mine) differed from Ceylon pearls
in ‘the large size of the nucleus in the pearl (where a nucleus is
present) and its characters, which are quite different from those of
the encysted parasites in the Ceylon Pearl-Oyster.” Now the
nucleus of a Mytilus pearl is generally about 0-5 mm. in diameter—
the size of the Trematode when contracted into a sphere. As the
Ceylon Cestode-parasite measures roughly from 0°5 to 1 mm, in
diameter, the nucleus of a Ceylon pearl, if composed of its
calcified remains, should if anything be larger, rather than
smaller, than that of a Mytilus pearl. And the characters of the
nucleus should not differ greatly—the dark opaque yellowish or
brownish substance formed by the decomposition and subsequent
calcification of the parenchymatous and muscular tissues of
a Trematode should not differ materially in appearance from the
analogous remains of a dead Cestode.
For purposes of comparison I figure below (text-fig. 33, A & B)
a Trematode pearl from Mytilus, from Foulney, Lancashire
(Preparation CIIT). A shows the pearl decalcified and examined
entire in oil of cloves, B shows the nucleus in section. In both
cases the foreign nature of the nucleus is obvious, quite apart
from the fact that in this preparation its Trematode character is
quite clear (which would, of course, not be the case where
decomposition had advanced considerably before calcification
commenced). The characters of this nucleus are quite different
from those of the pseudo-nuclei of Ceylon pearls figured in the
[18]
THE CEYLON PEARL-OYSTER. PEC
plates, the concentric stratification of the majority of which
never occurs in a Trematode nucleus, and could hardly be expected
in a Cestode.
Text-fig. 33.
A Mytilus pearl, from Foulney, near Piel, Lancashire, with a Trematode nucleus :
A, examined entire in oil of cloves, after decalcification ; B, the same in section.
In A the oral sucker and digestive ceca of the worm are distinctly visible.
In B the internal anatomy is still preserved. cw., cuticle; sp., spines on
same; dig., digestive cecum ; skr., ventral sucker; at dand g ave dark masses,
which may well represent the remains of the yolk-glands and gonads;
nac., nacre. C,a Mytilus pearl of non-Trematode origi, from Plymouth.
Here the nucleus is, as in many Ceylon pearls, a minute group of granules.
A X20; B xX 70; € xX 20.
As Mr. Cyril Crossland, Marine Biologist to the Sudan Govern-
ment, is quoted by Professor Herdman (Report Ceylon Pearl
Fisheries, Pt. V. Pearl- Production, p. 3) as supporting the Cestode
theory, so far as M/. vulgaris in the Red Sea is concerned, I wrote
to him to ask him for further information. He replied, in
a letter dated December 9th, 1911 :—‘‘I never published any state-
ment that Cestode larvee caused pearl-formation in the Red Sea.
‘Lhe evidence to my mind is in need of revision. In all cases the
first result of excessive stimulation of the secretory epidermis of
the mantle is the formation of a dark brown horny material
[7.e. my amorphous substance.—H. L. J.].. How would this stain
in sections, and is it cellular like the horny material of the prismatic
layer? If so, would not a shrunken nucleus of such material
resemble the dry remains of a Cestode 2? This is a criticism which
I have had in mind several years, and have never put it to
the test.” From this it is clear that Mr. Crossland, though cut
off from the possibility of applying modern laboratory technique,
has arrived at much the same conclusion as that which I am
elaborating in this paper.
To summarise the supposed relation between Cestodes and
[19]
278 DR. WH. LYSTER JAMESON ON
Pearls, as described by Professor Herdman and Mr. Hornell, the
position is briefly this :—
1) Ceylon Pearl-Oysters were found to contain large
numbers of Cestode parasites which occurred simul-
taneously with pearls, but which did not necessarily
result in the formation of pearls.
(2) The nuclei of the majority of “ cyst-pearls” were
thought to be identified as consisting of the remains of
these parasites, though Mr. Hornell’s figures of such
nuclei are capable of other interpretation.
(3) No satisfactory evidence was adduced of the Cestode
having acquired a surrounding epidermal sac, such as is
normally formed around the pearl-producing Trematode
in Mytilus, though Prof. Herdman admits that this sac
is essential for pearl-production. ‘The first stages in the
supposed process are therefore purely hy pothetical and
unsupported by observation, besides pre-supposing an
abnormal departure from the parasite’s usual habit.
The evidence in favour of the theory is mainly that the more
highly infected the oysters are with these particular Cestodes, the
richer they are in pearls. Thus it was observed in 1904 (Report
ILL. p. 32) that the oysters from the North-West Cheval, besides
being the most extensively infected with Cestode-cysts were also
the richest in cyst-pearls. And, again, Mr. Southwell records
(40, p. 194), that
‘the infection of the very old oysters [with tapeworm-cysts ]
found on the Kondatchi Paar in 1908 was remarkably low,
and, as bearing practical proof that infection and pearl yield
are intim: ately” connected, it is interesting to note that the
pearl yield also was remarkably low, the valuation only
working out at about Rs. 18 per 1,000 oysters,’
These facts might be explained, however, on the assumption
that the conditions favourable to pearl-production are also favour-
able to Cestode infection.
Characters, Identity, and Life-Histories of the Cestode Parasites
of Margaritifera vulgaris.
Apparently the first announcement of the supposed relation
between the Cestode and pearl-production was made by Prof.
Herdman at his Royal Institution lecture on March 27th, 1903
(14). In this he says that he and Mr, Hornell have proved so
far “that in Ceylon the most important cause is a larval Cestode
of the Tetrarhynehus form.” Again, in the Report of the British
Association, Southport, 1903, p. 695, Prof. Herdman says: ‘“ The
parasite in the case of the majority of the cyst-pearls of Ceylon
is the larva of a Cestode which appears to be new, and will
be described under the name of ‘ 7'etrarhynchus unionifactor’” ;
and the pearl-inducing parasite is referred to throughout Prof.
Tlerdman’s Report under this name.
[20]
THE CEYLON PEARL-OYSTER. 279
But the worm specifically described by Shipley and Hornell as
Tetrarhynchus unionifactor on p. 88 of Part I. of Prof. Herdman’s
Report (Parasites of the Pearl-Oyster) and figured in plate il.
figs. 19 & 20, is a well-advanced TYetrarhynchus 6:5 to 7 mm.
long, which oceurs in and around the intestine of the Pearl-
Oyster; and, to say the least of it, it is doubtful whether this worm
isa later stage of the globular cysts, which Prof. Herdinan identi-
fied as the nuclei of pearls, and not an entirely distinct organism.
In order to avoid confusion of terms I am therefore giving
separate names to the larger and smaller globular Cestode larvee
which Herdman recognises, as it is calculated to lead to much
confusion of issues if these are referred to by the name of Tetra-
rhynchus unionifactor before their identity with it can be demon-
strated more satisfactorily. The arguments for regarding the
supposed pearl-producing parasites as distinct from Tetrarhynchus
unionifactor are set forth below. In the absence of satisfactory
evidence of their relation to the genus Z'etrarhynchus, I propose,
following Seurat (36), to whose larval Cestode, mentioned above,
they bear a close resemblance, to refer them to the genus Tyloce-
phalum* and to describe the larger and smaller forms respectively
as T'ylocephalum ludificans, sp. n., and T'ylocephalum minus, sp. 0.
Two well-marked sizes occur in these globular larve and they
are regarded by Herdman as distinct organisms (Report V. p. 21).
On the other hand, Southwell considers that the asexual repro-
duction, which he has occasionally observed, accounts for the
varying sizes of the larvee in the Ceylon Pearl-Oyster, and says :
‘Tam now convinced that these different sizes merely represent the
same species in different grades of development.” 1 am inclined
to share Prof. Herdman’s view that these two sizes are distinct
organisms. It may even prove that there are more than two
species represented. Indeed, I should not be surprised if further
research on fresh material were to show that both Z'ylocephalum
ludificans and 7’. minus are composite species.
Professor Herdman regards 7. ludificans as the earlier stage
of Tetrarhynchus unionifactor, and calls attention to its re-
semblance to Van Beneden’s ideal figures of the young of
Tetrarhynchus, while he treats 7’. minws as another species of
Tetrarhynchus in its earlier stages. Nevertheless, he seems to
have had suspicions that some, ‘at least, of these larve might be
Tylocephala, though he appears in the end to have decided that
they—and presumably with them Seurat’s larva—are a hitherto
unknown stage in the life-history of the genus Zetrarhynchus.
In the Preface to Part IL. of his Report he says (p. vi) :—
“Tt is possible that some of our Ceylon Pearl-Oyster
parasites may also belong to the genus Acrobothrium’
|7.e. the genus to which Seurat’s larva was then referred |,
“although poe more advanced ones are certainly Tetra-
rhynchids ”
* Linton (27 a), pp. 805-9, pl. ix. figs. 5-9. Type T. pingue, from spiral valve
of Rhinoptera quadriloba.
280 DR. H. LYSTER JAMESON ON
while in Part V. of the Report, p. 14, he and Hornell say :—
“Some of our Ceylon Pearl- Oyster parasites very closely
resemble the figures given by Giard” |i. e. of Seurat’s lar va]
‘“and possibly may also belong to the genus Cyathocephalus
| Tylocephalum|, although most of them are certainly Tetra-
rhynchids ” ;
and on pp. 16-17:
“Tt is possible, however, that more than one species of
Cestode is represented—one is certainly a species of Tetra-
rhynchus (Rhynchobothrius), and another is probably the
saine genus, or may possibly belong to Cyathocephalus ... .”
Later on, however (p. 20), Herdman and Hornell reject the
idea that the globular larvee may be Tylocephala or allied genera,
and, in discussing the opinions of Giard and Seurat on the
systematic position of Seurat’s larva, they say that they regard
the terminal invagination, not as a sucker with a papilla on its
floor, but as
“the opening in a hood or depression formed by the
sinking of the scolex into the front of its vesicle. The
changes of shape which we observed in this larva in the living
state, the protrusion and retraction of the papilla-like part
which we regard as the anterior end of the scolex, agree with
this interpretation. Consequently, we are of opinion that this
larval Cestode is not one of the Monobothria—that it belongs
to neither the Pseudophyllidea nor the Tetraphyllidea, but is
a young Tetrarhynchid belonging to the Trypanorhyncha, and
we give here (fig. 4) a series of diagrams in order to show
the positions that we suppose our ‘stages to occupy in the
development of such a form.”
Shipley and Hornell (Herdman’s Report IT. p. 80) call attention
to the resemblance of older examples of the larger larva (7'ylo-
cephalum ludificans) to Seurat’s form, and think there is little
doubt that they are at least generically the same (p. 82). Again,
Southwell says (39, p. 169) :
“Tt would certainly appear more probable, as well as
simpler, for this larva to develop into a Tylocephalum (as is
believed by Seurat) than into a Tetrarhynchus.”
Again, Southwell, speaking of the great scarcity of the adult
of Tetrarhynchus unionifactor in Elasmobranchs taken by trawling,
says (42 p. 130):
“Tt would almost appear that this fact in itself is sufficient
proof that the adult of the pearl-inducing worm is not
Tetrarhynchus unionifactor.”
But at the foot of the same page he reverts to the position
that it is a Tetrarhynchus.
[22]
THE CEYLON PEARL-OYSTER. 28)
It is strange how the TZetrarhynchus unionifactor theory,
once enunciated, has prevailed :—indeed nobody seems to have
seriously followed up the obvious clue given by Seurat’s discovery
of the supposed adult of his worm.
Prof. Herdman says in his Report, Part V. pp. 20-21:
“Shipley and Hornell in Part II. (p. 77) described and
figured various stages of the Cestode larve both from the
centre of decalcified pearls and also free in the tissues of the
pearl-oyster, but left it an open question whether the sub-
globular younger larvee |i. e. T'ylocephalum ludificans, n. sp.|
belong to the same life-history as the elongated older forms,
which are young Tetrarhynchids. If our arrangement of
the stages observed in the tissues of the pearl-oyster is
correct, and if all these larve belong to the same species,
then the interpretation we have given above brings us to
the conclusion that the larger of our two globular larve
belongs to the worm which Shipley and Hornell described as
Tetrarhynchus unionifactor in 1904.”
And, referring to some figures of J'ylocephalum ludificans on
pl. ui. (Report, Part V. Pearl-Production) figs. 1-8, he says
(p. 21):
“there can scarcely be any doubt (1) that they all belong
to the same life-history, and (2) that they are young Tetra-
rhynchids leading on to the stages shown in figs. 10 and 11.”
Prof. Herdman gives, in support of his theory, a series of
figures showing the hypothetical transition from 7T'ylocephalum
ludificans to Tetrarhynchus unionifactor (Report, Part V. p. 21).
Later, a younger Zetrarhynchus, 1 mm. in length, was found
in the stomach and alimentary canal of the oyster, which Shipley
and Hornell (Report V. pp. 87-88) regarded as probably an
earlier stage of Tetrarhynchus unionifactor, though possibly a
distinct form. <A single example of a still younger form, which
is figured in the Report on Pearl-Production (V., pl. 111. fig. 10),
and is described in the text (p. 22) as occurring ‘ encysted in the
liver” and in the explanation of the plates as “ from cyst between
stomach and liver,” appears to go still further towards linking
the two forms. This larva is referred to in the text as °53 mm.
long. Tylocephalum ludificans grows to a much greater size than
this without changing its characters ; thus the one figured by
Shipley and Hornell in the “ Parasites of the Pearl-Oyster”
(Report, Part IT. pl. i. fig. 12), and described as x 40, appears
from the size of the figure to be over 1°5 mm. long, and still
shows no sign of becoming a TVetrarhynchus. And T. ludificans
quite frequently measures | mm. in diameter. This discrepancy
in dimensions makes it hard to believe that they are the same
organism, and the gap between the Tylocephalum form, with its
round Balanoglossus-like scolex or ‘“‘ myzorhynchus,”’ and the
[23]
282 DR, H. LYSTER JAMESON ON
Tetrarhynchus form, with its complex proboscides, cannot be said
to have been satisfactorily bridged.
Herdman found the Vetrarhynchus form much scarcer than
the Tylocephalum form, and it appears from his Report, Part V.
p- 22, that the ratio of the latter to the former is about 200: 6.
Shipley and Hornell (Report, Part II. p. 79) give the ratio of
globular larvee to undoubted Tetrarhynchi as 100: 1.
Prof. Herdman’s suggested explanation of this, namely, that the
globular parasite only occasionally advances to the Tetrarhynchus
stage, requires, it seems to me, a greater effort of the imagination
than the hypothesis that the two worms are distinct forms.
It is hard to conceive of conditions that would lead a small
minority of Z'ylocephalum ludificans or T. minus to leave their
tough fibrous cysts in the peripheral tissues, and migrate to the
intestine, there to take on the Zetrarhynchus form. It seems to
me much easier to regard these as two (or three) distinct species,
and their simultaneous presence in one host as a case of parallel
infection.
In his latest paper (42, p. 129), Southwell, speaking of these
undoubted Tetrarhynchids, says :—
“These are by no means rare, and are in almost every
case confined to a particular part of the wail of the gut, about
one inch from the anus and on the terminal part of the gut.
They often occur in clusters of three or four. They are
small (about 1 mm.), but appear to be adult im every way,
save that strobilization has not commenced. This encysted
young Tetrarhynchid is quite dissimilar to the globular cysts
found in the same oyster. In the latter case, the larvee are
so young that the Cestodian characters are but ill defined.
In the former case, a normal and full-grown Tetrarhynchid
head is present. No stage or stages have been found inter-
mediate between them, and the evidence that they are both
stages in the life-history of the same parasite rests on circum-
stantial evidence and on evidence obtained by feeding
experiments.”
And with reference to these feeding experiments, which are
referred to below (p. 287), and in which Zetrarhynchi were found
in Sharks that had been fed on pearl-oysters, Mr. Southwell says
(p. 130) :—
“The mere fact that the adults were obtained by feeding
is in itself almost sufficient to prove that they are the
adult of the pearl-inducing worm, for it is difficult to believe
that their occurrence in the Ginglymostoma was a mere
coincidence each year.”
I think there is very good reason to believe that Southwell
did, in his feeding experiments, actually transmit Zetrarhynchus
unionifactor from the Oyster to the Elasmobranch, but it 1s
[24]
THE CEYLON PEARL-OYSTER., 283
difficult to escape the conclusion that the worms found in Gingly-
mostoma were derived from the Tetrarhynchus larvee in or around
the alimentary canal of the Oysters, and not from the globular
Tylocephala in the other tissues, to which Southwell refers when
he speaks of the “ pearl-inducing worm.” To dispute this view,
it would be necessary to demonstrate that the Zetrarhynchus-stage
was not present in the Oysters used.
Shipley remained throughout sceptical about the identity of
the supposed pearl-forming larvee with Tetrarhynchus unionifactor.
In Part Il. of Herdman’s Report, p. 86, he says it is most
improbable that the young larve grow into the Tetrarhynchus
larva. In their report on the Cestode and Nematode Parasites
from the Marine Fishes of Ceylon, Shipley and Hornell say
(Pt. V. p. 66) :—
“Tt seems increasingly probable that the pearl-forming
Cestode is a 7. unionifactor, but this has not yet been
proved.”
Shipley and Hornell, in Herdman’s Report, Part V. p. 98, offer
the following hypothetical life-history :—
“Of the given number of larvee which enter at a very
early stage into the body of the Oyster a certain number arrive
in the mantle and other tissues, acquire an ectodermal sac and
there encyst, and find a costly grave in the developing pearl.”
|The ectodermal sac around these parasites is so far purely
hypothetical and has never been demonstrated.—H. L. J.|
“The remainder, however, réach the alimentary canal and
grow and flourish there. When they attain the dimensions of
thestages described in Part II. they leave the alimentary canal
and encyst, usually upon the outer surface of the intestine.
Now they are too big for enclosure in a pearl, and they can
wait without anxiety for the advent of their second host
(Rhinoptera javanica), within whose intestine they rapidly
become sexually mature.”
It would seem to the present writer much simpler to set aside,
for a while, the hypothesis that Tylocephalum ludificans and
7’. minus are younger stages of a Tetrarhynchus, and to seek for
their adult stages among the members of the genus Tylocephalum,
or allied types described as new genera, occurring in oyster-eating
Elasmobranchs. Shipley and Hornell have already described a
number of these, which I give below :—
*+Tylocephalum (Tetragonocephalum) trygonis (Report, Part
Jil. p. 51 and Part V. pp. 48 & 83). Habitat: intestine of
Trygon walga and Aétobatis narinari. Diameter of head
0-03 mm.
*Tylocephalum (Tetragonocephalum) aétobatidis (Report, Part
III. p. 52 and Part V. p. 48). Intestine of Aétobatis
narinart. Diameter of head 1-5 mm.
284 DR. H. LYSTER JAMESON ON
tT Tylocephalum dierama (Report V. p. 59). Intestine of Mylio-
batis maculata. Diameter of head *6 mm.
Tylocephalum kuhli (Report V. p. 72). Intestine of Zrygon
kuhli. Head apparently about *5 mm. in diameter,
tT ylocephalum uarnak (Report V.p. 76). Intestine of 7rygon
uarnak and Trygon walga. Head apparently about 1 mm.
in diameter.
*?Cephalobothrium actobatidis (Report V. p. 44). Spiral valve
of Aétobatis narinari. Diameter of head ‘5 mm.
*tAKystocephalus translucens (Report V. p. 46). Intestine of
Aétobatis narinari. Diameter of head ‘4 mm.
*Eniochobothrium gracile (Report V. p. 64). Intestine of
Rhinoptera javanica, Head appears to measure about
‘4 mm. in diameter.
*rTiarabothrium javanicum (Report V. p. 67). Intestine of
Rhinoptera javanica, Head | mm. broad.
To these may be added two forms described by Mr. Southwell
(41 a), viz. :—
Cephalobothrium abruptum, trom the spiral valve of Pteroplatea
micrura. Head 1:2 mm. broad.
Cephalobothrium variabile, from the intestine of Pristes cuspi-
datus. Head 1 mm. broad.
The forms marked * oceur in hosts which are known to feed
on pearl-oysters. Those marked + I have been able to examine
through the courtesy of Dr. Shipley. It is impossible not to be
struck with the resemblance between the heads of some of the
above species and the parasites which Herdman associates with
pearl-formation. Compare, for example, the head of Cephalo-
Lothrium aétobatidis, figured in Part V.(Cestoda) plate 1. figs. 1-4,
with some of the figures of 7'ylocephalum ludificans in the chapter
on Pearl-Production (Part V. Pearl-Production, plate ii.) or
the heads of 7'ylocephala (Tetragonocephala) as figured on the plate
of Part ITI. (Parasites), and in thearticle on Cestodes in Part V.
(pl. v. figs. 76-7), with some of the figures in the article on the
parasites of the Pearl-Oyster in Part II. Or, again, compare the
section of 7'ylocephalum ludificans from the pearl-oyster shown
on Pl. XLVI. fig. 58, with the head of 7. warnak, Pl. XLVIL.
fig. 65, drawn from one of Dr. Shipley’s slides, asa representative
of the genus T'ylocephalum, taking into account the difference
that in the former the myzorhynchus is withdrawn within the
collar, whereas in the latter it is fully protruded. Or compare
Pl. XLVI. fig. 59, a section of 7. ludificans from the pear]-
oyster, with the head of Cephalobothrium aétobatidis, from one of
Dr. Shipley’s slides shown on Pl. XLVILI. fig. 66. Similarly,
compare figs. 58 & 59 with the worm shown in figs. 61 & 62 on
Pl. XLVIT., also from A étobatis narinari (the final host of Seurat’s
larva) =. Ithink the worm shown in figs. 60-64 is quite probably
t It is strange that the oyster-eating habits of this Ray do not seem to have
heen recorded in these Cevlon researches.
[26]
THE CEYLON PEARL-OYSTER. 285
the adult of 7'ylocephalum ludificans—in fact, the only difference
appears to be the presence of the four lateral suckers, which are
absent in the larva, but which may well not develop till its
transference to the final host.
Comparison of these figures makes one feel doubtful whether
the generic distinction between 7'ylocephalum and Cephalobothrium
is a valid one, or whether the conditions shown in figs. 58 & 65,
and in figs. 59 & 66, are not merely the expression of a uniform
type of myzorhynchus in different stages of contraction, as
suggested diagrammatically in the following text-figure.
Text-fig. 34.
Diagram illustrating the relationship between the condition of the myzorhynchus in
Tylocephalum and Cephalotothrium. A, a generalised scheme of a scolex
such as the Tylocephala of the pearl-oyster. B, by protrusion of the
myzorhynchus, the outer surface of the same being tense, the inner surface
thrown into folds, the Tylocephalum-form may be produced (compare
Pl. XLVII. fig. 65). C, the partial retraction of the myzorhynchus to form
a sucker-like disk gives the Cephalobothrium condition (compare Pl. XLVI.
fig. 59 and Pi. XLVII. fig. 66). D, the myzorhynchus retracted within
its collar, with its outer surface thrown into folds, as is characteristic of
many of the larve of Tylocephalwm ludificans found in the pearl-oyster, and
of the adult worm figured on Pl. XLVII. figs. 61-62.
It does not necessarily follow that any of the above mentioned
worms actually represents the final stage of Z'ylocephalum ludificans
or 7. minus, though I think there are considerable grounds for
regarding the worm shown at figs. 60-64 as the former; but it
certainly appears more probable that these final stages will be
found among this class of parasites rather than among the
Tetrarhynchi, and it is strange that the position that the Tetra-
rhynchus unionifactor hypothesis may be wrong has never been
seriously faced and a fresh start made on the above lines.
It is not known how T'ylocephalum ludificans and Tylocephalum
minus enter the Pearl-Oyster; but Hornell found, in tow-netting
on the Muttuvarattu Paar on the 19th November, 1902, a free-
swimming larva, 37 mm. long when extended, which is figured
in Prof. Herdman’s Report (Part II. Parasites of the Pearl-
Oyster, plate 1. fig. la-h). This larva certainly suggests an earlier
stage of Z'ylocephalum ludificans, and one of the chief difficulties
in the way of accepting it disappears if this worm is dissociated
from the genus Jetrarhynchus, the normal habit of which is to
enter the digestive canal with the food while still in the egg-
[27]
286 DR, HW. LYSTER JAMESON ON
stage. (The fact that the undoubted Vetrarhynchi in the pearl-
oyster occur in and around the digestive canal suggests that
they follow the normal course and are swallowed in the ¢ egg-stage,
and first hatch out in the intestine of the oyster. ) Mr. ‘South-
well states (Ceylon Marine Biological Reports, Part IV. No. 6,
p. 169, 1910) that this free-swimming larva has not been seen
since it was first discovered (see also 42, p. 127).
I may here mention that one of Prof. Herdman’s slides which
I examined shows an interesting phase in the biology of these
supposed pearl-inducing Cestodes which may have escaped him.
It shows a small Cestode, 0-12 mm. long, with myzorhynchus and
collar fully developed, clearly in the act of passing through the
tissues. This may possibly represent the young of either form,
when first entering the oyster, or it may be a case of voluntary
or accidental migration by Z'ylocephalum minus (Pl. XXXII.
fig. 1). Dr. Willey (48, p. 50) records a similarly free larva seen
moving about in the liver of a species of Venus.
To return to the life-history of the true Tetrarhynchus unioni-
factor, Shipley and Hornell have shown without doubt that the
adult sexually mature worm occurs in the Ray, Rhinoptera javanica
(Herdman’s Report V. Cestodes, pp. 65-66). The identification
of the final host as Rhinoptera javanica is announced by Mr.
Hornell in a postscript to his Report on the November Inspection
of the Pearl Banks, 1904 (20, p. 8). Mr. Southwell (42, p. 130)
gives Teniura melanospilos as another host.
Professor Herdman in his Royal Institution Lecture, and in
Pt. I. p. 12 of his Report, claimed the File-fish, Lalistes, as an
intermediate host ; but Shipley and Hornell, in Herdman’s Report,
Part II. p. 83, say that “a more minute examination, however,
renders the connection between the parasites of the pearl-oyster
and those of the file-fish a doubtful one”; and the immature
Tetrarhynchi found in this fish are described as distinct species
under the names of 7'e trarhynchus balistidis and 7’. pinne. Prof.
Herdman sums up the position in the article on Pearl-Production
(Report V. p. 24) by saying :—
“No fresh light has been thrown upon the _ possible
occurrence of an immature stage in alistes (which is eaten
by the large rays), and although that intermediate host may
not be necessary to the life-history, since the rays also feed
upon pearl-oysters, still there is nothing in the observed facts
to forbid the existence of such a stage, and it is not unusual
in Tetrarhynchids to have two fish-hosts, an intermediate
Teleostean which is devoured by a final Elasmobranch.”
Mr. Southwell’s subsequent investigations confirm Prof. Herd-
man’s view that Balistes occurs as a collateral intermediate host
or “earrier”; he says (42, p. 132):—“It is certain that my
encysted Vetrarhynchus unionifactor from Balistes is not the
same species as those described” (7. e. by Shipley and Hornell
(28)
THE CEYLON PEARL-OYSTER,. 287
from Lalistes); and he claims that they are “ exactly similar to
the encysted Tetrarhynchid found in the oyster ”—i. e. the true
Tetrarhynchus unionifactor, except that they are slightly larger.
Mr. Southwell is satisfied that they are derived from the oysters
eaten by Balistes, and thinks that they are derived from
both the genuine Tetrarhynchids in the Oyster’s intestine and
from the globular cysts in its tissues. He considers that if
- Balastes is eaten by an Elasmobranch, the young worms become
adult ; but Balistes is not a necessary host, it is merely a “ carrier.”
Johnstone (26 b) confirms the view that the Teleostean host is
a collateral one, and not a normal stage in the life-history, by his
recent researches on the European Tetrarhynchus erinaceus.
The adult stage of this worm occurs in various species of Skates
and Rays, and the first host is probably some Invertebrate.
Johnstone regards the frequent occurrence of a larval form of
this worm in Teleosts as a “ cul-de-sac” stage, due to the first
host being eaten by the wrong fish ; and as normally leading no
farther, but ending in degeneration.
Mr. Southwell has further shown (38) that the adult Zetra-
rhynchus unionifactor occurs also in the Shark, Ginglymostoma
concolor. ‘This fish was doctored with Male-fern and castor-oil,
and subsequently fed on pearl-oysters ; but Mr. Southwell does not
claim that the Zetrarhynchi were actually derived from these
pearl-oysters, though he is inclined to think they were. The
same experiment was subsequently repeated [Southwell (41)]
and Tetrarhynchus unionifactor was again found in Ginglymostoma
concolor ; and while Mr. Southwell admits that his results are not
altogether conclusive, it seems highly probable that the infection
was in fact induced by his feeding experiment. There is nothing,
however, to show that the adult tapeworms in Ginglymostoma
were derived from the globular cysts in the oysters; it seems
more probable that they were derived from the Yetrarhynchi
in the oysters’ intestines.
These elaborate experiments are, of course, chiefly of academic
interest, in the absence of proof (1) that the Vetrarhynchi are a
later stage of the globular cysts, and (2) that the latter are
concerned in pearl-formation.
To sum up, then, the gap between (a) the resting scolex
enclosed in its tough fibrous cyst in the connective tissues of the
Pearl-Oyster and strongly suggesting by analogy with other
forms—notably Seurat’s larva—a young Z'ylocephalum, awaiting
and ready for its final host to devour the tissues which contain it,
and (b) the equally expectant, but much larger, Vetrarhynchus
wutonifactor in the wall of the oyster’s intestine, has not yet been
bridged.
I set out below diagrammatically the conclusions of Herdman,
Hornell, Shipley, and Southwell, as to the probable life-history
of these parasites, and also, for purposes of comparison, my own
attempt at an interpretation of the facts.
[29]
DrAGRAm illustrating Prof. Herdman’s conclusions as to the
life-history of the parasites.
Species I. Vetrarhynchus unionifactor.
B C
? Globular cysts in
Hornell’s free- liver and connective
: K —_—-~}—__; “p ratow
swimming Te tissues of Pearl-Oyster
i (= Tylocephalum ludi-
arva.
7 pies ficans).
if
A ee This transition is
/ \ doubted by Shipley.
is yh \
/ \ D
Kgg, Larval Tetrarhyn-
mei hus wunionifactor in
hatching in cee if era
neighbourhood of ali-
sea. mentary canal of Pearl-
Oyster.
F E
Adult Tetrarhyn- Immature = Tetr-a-
chus unionifactor in rhynchus in Balistes.
alimentary canal of Y Thisstage is rejected by
Rhinoptera javanica Shipley, and is regarded
and Ginglymostoma as collateral or acci-
concolor. dental by Southwell.
Species IT. “ Tetrarhynchus sp.”
G
Smaller globular cysts
in connective tissues of
Pearl-Oyster (= Tylo-
cephalum minus).
Southwell considers
this the same species
as “C” above.
Ja
Possibly the smaller
Tetrarhynchus found
in the intestine of the
Pearl-Oyster, if it is
distinct from T. unio-
nifactor.
/
y
[30]
DrAcram illustrating my hypothesis of the relations of the several
forms and stages of Cestode larvee described in Herdman’s
Report.
(The letters correspond to those in the above diagrams.
Those
marked A’, A”, B’, and J' are regarded as parallel stages to
A, B, and J.)
Species I. Tetrarhynchus unionifactor.
7X
oo, (?) swallowed by
Pearl-Oyster ; hatch-
ing out in intestine to
\
\
\
\
x
Eoo
become
— >
F
D
Larval Tetrarhyn-
chus unionifactor, in
and around the ali-
mentary canal of the
Pearl-Oyster.
¥
Adult Tetra rhynchus
unionifactor
mentary canal of Rhi-
noptera javanica and
Ginglymostoma
color.
in ali-
con-
Species II. Tylocephalum ludificans.
B
(?)
Hornell’s free-
swimming
larva.
vA
wee
La
A M
px A q Cc
ee Se .
Egg, (?) hatching in~ Se Globular cysts, T'ylo-
sea-water to become B cephalum ludificans,
or (?) swallowed by = in liver and connective
Pearl-Oyster to be- tissues of the Pearl-
come C, NY Oyster.
\
x ¥
J
An adult Tyloce-
phalum-like form in
one of the oyster-eat-
ing Elasmobranchs;
probably Aétobatis
narinari.
Proc. Zoou. Soc.—1912, No. XIX. 19
[31]
290 DR, H. LYSTER JAMESON ON
Species ILL. Tylocephalum minus.
B’
(?)
A free-swimming larva,
hike B above, only
smaller,
N
A” : :
ae. The smaller globular
Joo ( é Yin es
Egg, (?) hatching in cyst, Tylocephalum
sea-water to become B,——_— == ia minus, in connective
or (2) swallowed by tissues of the Pearl-
oyster to become G. —\ Oyster.
X ¥
A
An adult = Tyloce-
phalum-like form, in
one of the oyster-eat-
ing _ Elasmobranchs.
Scolex probably about
‘2 mm. in diameter.
(5) Descrierion OF THE TWO GLOBULAR CEsTopE LARV# FROM
THE CEYLON PEARL-OYSTER.
IT append the following descriptions. They are certainly
incomplete, being based on examination of preserved material
and on the descriptions of previous writers :—
Tylocephalum ludificans, sp.n. (The larger globular larva ; the
supposed pearl-producing worm.) (PI. XLVI. figs. 58 (type)
& 59.)
The type, fig. 58, is in Slide 94 in Prof. Herdman’s Collection.
Tetrarhynchus unionifactor (young) Herdman. (For other figures
see Herdman’s Report, Part I]. Parasites of the Pearl- Oyster,
pl. i. figs. 12 & 13; Part V. Pearl-Production, pl. 11. figs. fat ote
& 176, pl. ii. figs. 1-5, 6, 7, 8, & 9; also Part V. p. 21.)
Globular Cestode larvee, with rostrum or myzorhynchus (Linton)
retractile within a denticulated collar. Form more elongated
when liberated from capsule; length 0°5 tol‘) mm. Average
diameter of seven specimens sectioned on Prof. Herdman’s slides
and examined by the writer, 0°78 mm.
[32]
THE CEYLON PEARL-OYSTER. 291
Myzorhynchus uniformly muscular, without obvious division
into muscular tracts; retractile within an annular collar; in
section it may appear either conical, Jenticular, or flattened,
concave and sucker-like ; protrudes as a conical papilla when in
locomotion. ‘This anterior muscular region, including the collar,
is about one-third of the total length of the larva when extended.
The whole myzorhynchus can be protruded, the collar then
forming an annulus around it.
Collar or cephalic sheath muscular with denticulated cuticle,
the denticles tricuspid. (Herdman’s Report, Part II. (Shipley &
Hornell, Parasites of the Pearl-Oyster) pl. i. figs. 10,11, & 14,
pl. i. fig. 18; also Pt. V. (Pearl- Production) pl. iii. fig. 9.)
The denticles measure from 3 « to 5 u in diameter.
Hinder part of the larva centrally parenchymatous, the
parenchyma containing the calcareous corpuscles characteristic
of Cestode larvee, peripherally more muscular.
The hinder part of the body is covered by a thick, radially
marked epicuticle, permeated by numerous closely-set tubuli,
and suggesting on superficial examination a coat of cilia. This
epicuticle varies in thickness but is generally about 0:03 mm.
thick, and the true cuticle lies under it.
This form is distinguished from the next described worm by its
larger size (Her dman gives the size as about six times that of the
smaller form), the undivided musculature of the myzorhynchus,
and the wider and more open character of the collar-sheath of the
myzorhynchus in the resting-stage.
Habit. Resting in spherical tibrous cysts, derived from the
connective tissue of the host, in the Ceylon Pearl-Oyster,
Margaritifera vulgaris. Most frequent in the visceral mass,
notably the liver.
Habitat. Gulf of Manaar (Herdman & Hornell). Trincomalee
( Willey).
The following is a description of a worm which I regard as
in all probability the adult of this larva. The single specimen
was obtained from the spiral intestine of Aétobatis narinari, by
Mr. Hornell, on 4th January 1905, and had apparently been
overlooked by Mr. Shipley among some duplicate specimens of
Kystocephalus translucens, along ‘with which I found it when
examining Dr. Shipley’s material. After it had been cleared and
examined as a transparent object, Dr. Shipley very kindly allowed
me to have sections cut from it to compare with those of the
larva in the pearl-oyster.
(2) Adult of Lylocephalum ludificans, Spa pe , (Pls: Xb Vaes&
XLVII. figs. 60-64.) Length 12mm. Head 0°6 mm. long by
0-5 mm. broad ; pyriform, slightly broader in front than behind ;
transition from head to neck not very sharply defined. The
myzorhynchus in this specimen is retracted within its sheath, as
is usually the case with the larva in the pearl-oyster; it is about
*3 mm, in diameter. Around the head are four marginal suckers
about *125 mm. in diameter. Proglottides about 140 i in number,
increasing but little in breadth from before backwards ; they
ios
292 DR. H. LYSTER JAMESON ON
begin to increase notably in length from about the 85th back-
wards. The largest hindmost segments are about *5 mm. long,
and slightly longer than broad (fig. 64). The armature of the
collar @ (in ‘figs, 61-63) is similar to that of the larva. In section
(fig. 62) the myzorhynchus is seen to be retracted im such a way
that its anterior surface is thrown into folds, thus resembling the
condition of the larva shown in fig. 59. The only point in which
the head of this worm appears to differ from the larva in the
pearl-oyster is in the presence of the four marginal suckers, which
may well be a feature first acquired in the final host.
Tylocephalum minus, sp. n. (Plate XXXIIT. fig. 2.) (The
smaller globular larva, which Prof. eran thinks may
also be concerned in pearl-formation.)
(Tetrarhynchus sp., Herdman.)
For other figures see Herdman’s Report (Pearl Production),
Part V. pl. ii. figs. 1-3, 17.4, 18-22; also text-figure 3, p. 19.
Diameter of resting parasite in cyst from 0:07 to 0°2 mm.
Average diameter of 40 examples shown on Prof. Herdman’s
slides and measured by the present writer, 0°14 mm. Body sub-
globular, consisting, as in 7’. ludificans, of an anterior muscular
and a posterior parenchymatous part, the anterior muscular
portion (myzorhynchus) consisting of a conical papilla in a ecup-
flask-shaped depression formed by the surrounding muscular
collar or sheath. As a rule, in preserved specimens, the opening
of this depression seems relatively narrower, and the papilla more
conical and less flattened than in the previous species. The
musculature of the myzorhynchus shows, in some examples
a tendency to break up into four longitudinal tracts. In
young examples the myzorhynchus may be barely differentiated
Cuticular spines are present on the collar, but they are smaller
and relatively finer than in 7”. ludificans. The epicuticle is about
°O1 mm. thick.
This form is distinguished from 7’. ludificans by its smaller
size and finer armature of the collar, and by the tendency of the
myzorhynchus musculature to break up into four strands. It is
regarded by Southwell as the same species as 7’. ludificans.
Habit. Resting in spherical fibrous cysts in the connective
tissues of Margar nitifer a vulgaris, occurring in the visceral mass,
mantle, gills, ete.
Habitat. Gulf of Manaar.
Prof. Herdman, while he regards the form here named
T. ludificans as the pearl-producer par excellence, considers that
the present species too ‘*may occasionally form the nuclei of
pearls” (Report V. p. 22).
Particulars of the structure of both these forms are given on
pp. 79-82 of Part IT. of Prof. Herdman’s Report.
[34]
THE CEYLON PEARL-OYSTER. 293
(6) OBservaTions oN THE SrrucruRE oF THE FiBrous Cysts
SURROUNDING THE CESTODE LARV& IN J/ARIGARTIFERA
VULGARIS,
T may here add a few notes on the structure of the investing
eysts of Tylocephalum ludificans and 7’, ninus, based wpon my
examination of Professor Herdman’s slides and Dr. Kelaart’s
material,
In the earliest stages the cyst may be scarcely differentiated
from the surrounding tissue, and about 0:01 or 0-02 mm. thick.
This condition I find specially associated with a little-developed
phase of the smaller larva 7. minus, measuring 0°08 mm. in
diameter, and resembling B in figure 4 on p. 21 of Part V. of
Herdman’s Report. In such thin cysts the nuclei of the fibres
are distinct, though hardly more so than those of the general
connective tissue of the oyster. One or two examples at this
and later stages were found in the muscular tissue without any
surrounding cysts at all, beyond a little of the interstitial tissue
of the muscle-bundles (Pl. XX XIII. fig. 2). As the fibrous
capsule becomes thicker the nuclei appear ‘at first to become more
abundant, and this may well be associated with the growth and
multiplication of the fibres. As a rule, the thicker cysts (0°2 mm.
thick and over) seem to be less densely nucleated, and may even
show very few nuclei, especially when they become highly areolar
and edematous. The outer part of the cyst is usually ordinary
areolar connective tissue, with branched and anastomosing fibres
passing over, often quite imperceptibly, into the general con-
nective tissue of the body, such as occurs between the tubules
of the liver. The cyst is, however, typically lined with several
layers of more regular parallel fibres, with abundant nuclei. In
some cases the fibres seem to coalesce to form a dense almost
eristly substance, without obvious nuclei,
The nuclei of the fibres are long and narrow, and are situated
on their outside edges.
In some cases the cyst appears to be entirely without nuclei,
and in such cases the fibres are often very thick, measuring as
much as 10 or 15 yu in diameter.
There is never, so far as I can see, any trace of a lining
epithelium, though the cyst may be lined with a layer of granules,
possibly derived ‘from the Cestode or from the leucocy tes of the
blood.
In certain cases large dark-staining bodies were seen in the
aveole of the fibrous connective tissue of the cyst, which suggested
parasitic Sporozoa, but the preparations did not allow of detailed
examination,
A typical section of the cyst of the smaller parasite,
Tylocephalum minus, is shown on Pl, XX XIII. fig. 3.
This condition of things is very different to that which is found
in the case of the pearl-inducing Trematode of J/ytilus described
in my paper (25). Here the parasite is surrounded by an
[35]
294 DR. H. LYSTER JAMESON ON
epidermal sac (/. ¢c. pl. xv. fig. 5) of the same nature as the outer
shell-secreting epidermis. In such a case it is easy to understand
how the parasite, when it dies, becomes encased in a pearl, laid
down, layer upon layer, by this epithelium *.
(7) MAvTERIALS AVAILABLE FOR THE PRESENT INVESTIGATIONS.
I have throughout these investigations been seriously handi-
capped by the extreme difficulty of obtaining material. Many of
the points which remain obscure could probably be cleared up if
IT could obtain properly preserved specimens of pearl-bearing
oysters from the Gulf of Manaar. Unfortunately, I have been
quite unable to obtain these.
I endeavoured to do so through the Ceylon Company of Pearl
Fishers, Ltd., and Mr. Southwell, but without success, Mr. South-
well replying that there were no oysters on the banks and that
his own preserved material was finished. The Company, however,
kindly forwarded to me a suggestion made by Mr. Southwell to
the following effect :—
“As it is probable Dr. Jameson requires Ceylon pearls
(with the particular parasite giving rise to same), I would
suggest that in order to ensure that the pearls are from
Ceylon that they be bought here. I shall be glad to pur-
chase pearls for Dr. Jameson, if he will give me some idea
what to get and how much to spend.”
J gladly availed myself of this offer, and asked Mr. Southwell
to spend five pounds in the purchase of ‘“ cyst-pearls.” For this
sum he procured from a local jeweller a parcel of 21 small ‘ fine”
pearls, which I received in February 1911.
* T must here incidentally refer to a quite erroneous interpretation which was
placed upon the expression of my views as to the origin of the sac in Mytilus in my
paper above referred to.
My account of the development of this sac on p. 149 appears to have been taken
by Herdman and by Boutan (3 & 4) toimply that I thought the sac arose from the
mesoblastic connective-tissue elements of the mantle. As I explained in a letter to
Prof. Herdman, which he was good enough to publish, as showing my views, on
p. 9 of Part V. of his Report, I never had any doubt that the sac was a true
epidermis. What I wished in my paper to emphasize was that in Mytilus it
appeared to arise independently of, and not in continuity with, the outer epidermal
epithelium, perhaps from in-wandering epidermal cells, perhaps from more deeply
seated elements of epiblastic origin, some of which (e.g. certain flask-shaped glands in
Margaritifera, see Pl. XLI. fig. 33) appear to project below the basement-membrane.
Had I dreamed that I should have been suspected of attempting to promulgate
heretical views on the doctrine of the immutability of the three primary germinal
layers, I would have been more cautious in the choice of my phrases. But even if
my wording in that paper was unintentionally somewhat ambiguous, my résumé of
my work in ‘ Nature’ (26) should have cleared away any misconception, for in that
paper I definitely stated (p. 280) that “a true pearl is laid down in a closed sac of
the shell-secreting epithelium, embedded in the subepidermal tissue of the mantle
and completely cut off from the outer epithelium itself..... Such a sac, with its
contained pearl, may be compared to a human atheroma cyst.’ I have not yet
reached the stage at which I can add to what I said in 1902 about the actual mode
of origin of the epidermal sac in Mytilus, but I hope before long to be able to
contribute some more facts on the subject.
[36 |
THE CEYLON PEARL-OYSTER. 295
I then tried the Colombo Museum in the hope of getting some
oysters with pearls cm situ, but Dr. Pearson had no preserved
material to spare. I tried to obtain material from Madras from
Mr. Hornell, but he wrote me, in January 1911, that his own
material was exhausted, and that he would not be able to obtain
any more till the next inspection, a year later. However,
H.H. the Jam Saheb of Nawanagar most kindly sent me some
preserved specimens of this species with pearls in situ from the
Gulf of Kutch, and I hope, in a later publication, to be able to
put forward some observations on the actual process of pearl-
production, based on these.
The followi ing material was available for these investiga-
tions :—
(i.) Twenty-one pearls bought in Ceylon. It is, of course,
possible, though not probable, that some of these originally came
from elsewhere, e.g. the Persian Gulf vid Bombay, but they, or
at least the great majority of them, were certainly derived
from J/. vulgaris, the pearls of which have a characteristic
colour and lustre quite different from that of the pearls found in
M. margaritifera and M. maxima.
They were small ‘“ fine pearls,” mostly spherical, a few oval or
slightly lenticular. One wasa brown pearl formed in the mantle-
margin from the prismatic substance. They were all decalcified
and examined whole, cleared in oil of cloves, and drawn. They
were then sectioned (except in the case of three examples which
were preserved whole). Their nuclei were in no cases Cestodes ;
they usually contained a cavity with a few granules surrounded
by spheerocr ystal-like matter, allied to or identical with the
“ repair-substances ” described below. In several cases, however,
the actual nucleus was a grain of sand. These specimens are
preserved as preparations XL, XLII, XLII, XLIV, XLV,
SCV DI a GEV) LEV a LAY Be: GeV, p,
biVon Gi ae LiVee;. LEV a; LIV 1, LEV s,.and LIV «
(Pls. XLI.-XLITI. figs. 35-45 and Pls. XLV., XLVI. figs. 50-57).
(ii.) Dr. Kelaart’s Material in the British Museum.
In 1901, when I was investigating the origin of pearls in
Mytilus, Mr. E. A. Smith, 1.8.0., allowed me to examine five old
specimens of the Ceylon Pearl-Oyster from Dr. Kelaart’s
collections in the British Museum. Mr. Smith very kindly
allowed me to make further use of some of this material for the
present investigations.
The specimens are labelled :—
“1 specimen of pearls in ovaria,
3 specimens of pearls in mantle,
1 specimen of ova of Entozoa in liver of J/eleagrina
margaritifera.”
The specimen with‘ pearls in ovaria” was a pearl-oyster with
[87
296 DR. H. LYSTER JAMESON ON
a quantity of clustered pearls, mostly of the baroque and seed-
pearl classes, in the visceral mass. The three examples with
“pearls in mantle” showed pearls, chiefly in the regions of the
levator muscles, though some were in the non-muscular parts of
the visceral body-wall. The specimen with ‘ova of Entozoa in
liver ” is interesting, as showing the Cestode, Tylocephalum
ludificans, in its whitish fibrous pearl-like cysts, which on super-
ficial examination suggest “eggs.” It was in this specimen,
in 1901, prior to Prof. Herdman’s departure for Ceylon, that I
first became acquainted with these larve, which Prof. Herdman
identified as the cause of cyst-pearls. The few observations that,
[ was able to make at that time led me to the conclusion that
there was no evidence that this parasite was concerned in pean'-
formation *, a conclusion that I have, so far, seen no sufficient
cause for modifying.
Owing to their age, the state of preservation of these specimens
was naturally somewhat defective, and for real detailed histological
work upon the pearl-producing tissues they were quite useless.
Many of the pearls in these specimens had fallen out of their
sacs and lay in the bottom of the jar. Some of these, along with
others picked out of the tissue, numbering 22 in all, were
decalcified and examined in oil of cloves, and six of them were
then sectioned and further examined. [Preparations XIV, XV,
OVE LX hie, aX Kite, TXeXt ys (Bis? Rex Revell Nek val nl,
figs. 16-18 and Pl. XLIV. figs. 46-48). |
A large piece of tissue in the wall of the visceral mass,
measuring about 5x5x4 mm., and containing no less than
16 pearls, was cut out from the specimen with “ pearls in ovary,”
decalcified, stained with borax carmine and indigo carmine, and
sectioned [Preparation XXVIII (Pl. XXX VII. figs. 14, 15)].
These pearls were all of the class which I refer to provisionally
(see below) as muscle-pearls, and were mostly formed around
central cavities.
(iii.) Unlabelled Material in the British Museum.
Mr. Smith also allowed me to examine two unlabelled speci-
mens of Margaritifera vulgaris in the British Museum, the
history of which is unknown. One of them was with the example
in spirit now on show in the Museum, and was accompanied by
its shell. It is from this example that preparations XX VII and
XXIX were cut. It contained a large number of muscle-pearls
and what Prof. Herdman calls “calcospherules” in the left
mantle-lobe, and in the region of the adductor muscle on the left
side. The other example had been removed from its shell.
It contained a large number of clustered pearls, of all sizes, in
the right mantle-lobe. The tubes in which the specimens were
preserved contained also a lot of loose pearls which had dropped
out of both these specimens.
* In 1902 (25), p. 149, I pointed out that Cestode larve were not surrounded by
a pearl-sac.
[38]
THE CEYLON PEARL-OYSTER. 297
From the first of these specimens the following preparations
were made :—
(a) Preparation XX VII, a piece of tissue cut from the border-
land between the mantle and the adductor in the first of the
above specimens. This piece measured about 7x5 x 4 mm., and
contained 36 small pearlsand numerous so-called “calcospherules.”
The preservation was so bad that no differential staining of
the soft tissues could be obtained, all parts reacted alike to the
stains used. [Preparation XXVII (Pls. XXXVIII., XXXIX.
figs. 19-21, Pl. XL. figs. 24—27.)]
(b) Preparation XXIX was a piece of the mantle of the same
individual near themargin, containing 17 so-called“ calcospherules,”
one of which is becoming coated over with nacre (Pl. XX XIX.
figs. 22 & 23). The figures were made from the whole object—
fig. 22 representing it as it was before decalcification, fig. 23 after
it had been decalcified ; both as seen when cleared with oil of
cloves. The preparation was then sectioned, but the state of pre-
servation did not allow of the relations of the “ calcospherules ”
to the tissues being investigated in this instance. A piece of
tissue was also cut from the second of these specimens, decalcified,
examined entire, and sectioned. It contained about 20 small
pearls and numerous so-called “ calcospherules.” [Preparation
XXIV.|
Forty pearls, of varying sizes, some lying loose in the bottoms of
the jars containing the specimens, others taken from the tissues,
were decalcified and examined in oil of cloves. Of these, six were
sectioned and further examined. [Preparations XXIII, LXIIT
(a, B, & L), and LXVI (4&1) (Pls. XXXIX.-XLI. & XLIV.
figs. 21 a, 28, 31, 32, 49).]
All the pearls from these specimens I refer to the class called
by Herdman ‘“ Muscle-Pearls.”
(iv.) Three Specimens of the Pearl-Oyster collected by Professor
Herdman in 1902.
Prof. Herdman, at the request of the Ceylon Company of
Pearl Fishers, Ltd., very kindly allowed me to examine his
material (see (v.) below) and handed me three specimens of the
Pearl-Oyster, each of which contained a small “ muscle-pearl ” at
the point of insertion of one of the levators of the foot. The pieces
of tissue containing these three pearls were cut out, decalcified,
and sectioned [ Preparations IV, VI, and VII (Pl. XX XV. fig. 8) |.
Although these specimens had, apparently, been preserved
in formalin, which is not the most satisfactory preservative for
histological purposes, they showed quite a lot of histological
detail, and enabled me to form some idea of the mode of origin of
muscle-pearls, and of the curious cyst-like bodies which precede
them.
(v.) Professor Herdman’s Slides.
As stated above, Prof. Herdman very kindly allowed me
to examine his slides, which he sent to me a few at a time.
[39]
298 DR. H. LYSTER JAMESON ON
Most of these slides were preparations showing the parasitic
Cestodes in the tissues of the oyster, but there were also a number
of preparations of pearls, sectioned in sitw in the tissues, showing
in all about 25 pearls, 21 of which showed their nuclei more or
less distinctly. The nuclei of these pearls were of very different
characters, but in no case could I identify a Cestode larva in the
centre of a pearl.
(vi.) Three Specimens from the Persian Gulf.
In September 1903, Mr. J. Caleott Gaskin, Assistant Political
Agent at Bahrein, Persian Gulf, sent me 32 specimens of
Margaritifera vulgaris from Bahrein preserved in alcohol. Out
of 20 of these that I opened, 3 contained pearls, which, from their
position, could obviously be classified as “* eyst-pearls ” (Herdman).
‘wo contained a single pearl each, that in the first being about
2°5 mm. in diameter, situate in ye left mantle-lobe, above the
anterior end of the attachment of the gills | Preparation LXIV Al,
that in the second [ Preparation LXIV B] being about 1 mm. in
diameter and situate in the body-wall over the stomach. The
third specimen had two small pearls, about 2 mm. apart, in the
wall of the visceral mass, away from all muscle-impressions
[|LXTV coc], All these pearls were decalcitied in situ in the tissues
and sectioned. Their centres are described below.
In addition to the above the following pearls were decalcified
and examined. More detailed particulars are given under the
descriptions of the centres of individual pearls, given below :—
(vu.) Dry unlabelled pearls, probably from Ceylon, in the
British Museum, three examples were decalcified.
(vill.) Mixed lot of pearls; given to me by Mr. Max Mayer,
mostly from Margaritifera vulgaris ; 115 were decalcified, of these
8 were sectioned,
(ix.) A collection of pearls from the last Ceylon pearl fishery,
given to me by Mr. E. Hopkins. Fifteen were decalcified,
and four of these were sectioned.
(x.) A collection of pearl-oysters, with pearls i sitw, from the
Gulf of Kutch; these are referred to above. Up to the time of
writing, 18 pearls from these specimens have been decalcified,
and 13 of them sectioned.
(xi.) Two pearls from Margaritifera vulgaris, from the
Mediterranean, given to me by Professor Raphael Dubois.
(xi1.) Five weotle from Margaritifera vulgaris, from New
Caledonia, given to me by Professor L. G. Seurat.
(xi.) A pearl from Margaritifera vulgaris, from Madagascar,
given to me by Professor Seurat.
(xiv.) Two pearls from Margaritifera vulgaris, from Papua,
from the Imperial Institute.
[40]
THE CEYLON PEARL-OYSTER, 299
(xv.) Twenty pearls from Placuna placenta, from Lake Tam-
palakamam, Ceylon, from the Imperial Institute.
(xvi.) About a dozen pearls from Margaritifera margaritifera
var. cumingii, from the Gambier Archipelago.
In the course of these observations, apart from studies on the
structure and formation of pearls in other forms, 356 pearls
derived, with perhaps a few exceptions, from Margaritifera
vulgaris, chiefly from Ceylon, have been decalcified and examined,
175 of these having been studied in sections.
(8) Mrrnops.
For decalcification, whether the pearls were free or in siti,
preserved in alcohol or dry, I found alcohol of about 50 per cent.
strength, to which a few drops of nitric acid had been added, was
the best. Of course, a preserved pearl never decalcifies as well as
a fresh one. In the case of dry pearls, where only the nucleus
and central parts are required for examination, it is often
an advantage, during decalcification, to strip off the outer layers
of conchyolin, thus facilitating the penetration of the reagent.
Bubbles of carbon dioxide, generated in the process of decalci-
fication between the conchyolin-layers, cause a great deal of
trouble, especially in old dry pearls, where the conchyolin seems to
be particularly leathery and impermeable. Such bubbles often
greatly distort the normal structure of the pearl, as seen in section,
by tearing the conchyolin-layers apart and causing great spaces
betweenthem. The most suitablereagent for expelling the bubbles
is absolute alcohol, in which the decalcified pearl is placed for
a few days. In some cases, however, it was necessary to extract
the gas under an air-pump.
For staining decalcified pearls hematoxylin was used, also
borax carmine. Sections of the pearls in the tissues were
stained sometimes with borax carmine and picro-indigo-carmine ™*,
sometimes with hematoxylin and eosin or orange, occasionally
with other reagents.
(9) STRUCTURE OF THE SHELL-SUBSTANCES.
The shell of Margaritifera consists of the following parts :—
(i.) the outermost layer or so-called Periostracum ;
(ii.) the prismatic layer, forming with (1) the ‘ back” of the
shell, the fragile, dark-coloured “lip,” and the lappet-
like processes of the margin ;
* Borax carmine (Grenacher’s) in bulk :—
Picro-indigo-carmine as under, on the slide.
A. Saturated solution of picric acid in 90 per cent. alcohol.
B. Saturated solution of indigo-carmine (Grubler) in 70 per cent.
alcohol.
1 part of A, 2 parts of B, 6 parts of 70 per cent. alcohol.
[41]
300 DR. H. LYSTER JAMESON ON
(ili.) the Naere or Mother-of-Pearl, forming the lining and
the bulk of the shell ;
(iv.) the Hypostracum, the substance to which the muscles
are attached by a specialised epithelium ;
(v.) the Hinge Ligament.
The mass of the shell is further divisible chemically and
microscopically into an albuminoid substance called “ conchyolin ”
and erystalline carbonate of lime deposited therein. Roémer’s
‘areful observations (32) have shown beyond a doubt that there is
a sharp separation between these two substances : the conchyolin
forming an alveolar framework, in the chambers of which the
salts are deposited ; the structure of the calcium carbonate being
crystalline, its form being determined by that of the spaces in
which it is deposited.
The ratio of conchyolin to caleareous salts differs in different
parts of the shell. Thus Rémer (32) has found in Margaritana,
the fresh-water pearl-mussel, that the organic substance con-
stitutes 1°47 per cent. by weight of the prismatic substance, but
only *64 per cent. of the nacre. This is most interesting as
giving support to the theory of the present writer, enunciated
below, that the different structures of the different forms of
shell-building substances, normal and pathological, are in part
a function ae the proportions in which these two constituents are
secreted by the tissues of the mollusc.
To turn now to the details of the structure of the several
constituents of the shell.
(1.) The Periostracum.
The origin of the Periostracum can best be understood if we
consider ae those forms which live in fresh or estuarine water,
or are otherwise subjected to conditions which render nece ssary
. thick cuticle-like layer to defend them from the erosive action
of organic acids derived from decomposing animal and vegetable
mmatter (e.g. the Unionidee and J/ytilus). The periostracum
in such cases has been described fully by several authors,
e.g. Biedermann (1), Moynier de Villepoix (28), Tullberg (47),
Ehrenbaum (9), Felix Miiller (29), Stempell (44), List “(27 b),
ete.
In these cases the periostracum is composed of two constituents.
The outermost layer is probably formed as a true cuticle directly
by transfor mation or cuticularisation of the outer surfaces of the
cells of a specialised epithelium in the inner (axial) face of a deep
groove which runs along the mantle-margin, and which has been
called by Moynier de V ‘illepoix (28, p. 18) the “ fente marginale.”
This marginal groove divides the mantle-margin into an inner
and an outer lobe, the former being pigmented and sensory, the
latter being a part of the shell- secreting apparatus. This outer
[42]
THE CEYLON PEARL-OYSTER. 301
layer of the periostracum is closely adherent to the specialised
epithelium, so that secondary thickening, if it takes place (and
my own observations on Mytilus and Modiola lead me to think
that it does so to some extent, a view which is held also by
List, 27 6, p. 55), differs from that of all other parts of the shell
(including the inner layers of the periostracum) in that it
is secreted from outside or centrifugally with respect to the
body of the animal and the shell, instead of from inside or
centripetally. It would, indeed, seem as though there were
morphological grounds for restricting the name periostracum to
this particular layer of the outer cuticle-like substance, or, failing
that, for introducing a term which would separate it more sharply
from the more bulky inner layers. The structural distinctions of
this layer are well shown by Romer (32) fig. 25 (Margaritana), by
Moynier (28) fig. 50 (Mytilus), by Tullberg (47) Taf. iv. fig. 3,
fig. 4d (Mytilus), and by List (27 6) in the Mytilide generally.
The greater part of the periostracum, however, is Jaid down
centripetally, layer upon layer, by the epithelium on the outer side
of the marginal groove (i.e. on the inner side of the outer of
the two lobes of the mantle-margin, Tullberg (47) p. 27). It is
stratified, and in Mytilus contains, near its outer limit, a charac-
teristic layer of largealveoli. The stratifications of this substance
have been shown by Romer to correspond to layers of minute
alveoli (32, fig. 25).
Internally the inner layers of the periostracum pass over into
the conchyolin framework of the prismatic layer.
In some forms, e. g. Anodonta, the distinction between the two
constituents of the periostracum are emphasized by the outer
layer being much greater in area than the inner ones, and being
thrown into folds upon which the inner layers lie unconformably.
The Mother-of-Pearl Oysters (together with such forms as
Ostrea and Pecten) differ from the types to which the above
description refers in the fineness of the periostracum and in having
much more freely retractile mantle-margins. In sections of the
decalcified shells of the Mother-of-Pearl Oysters it is difticult—
indeed, I might say impossible—to differentiate the periostracum
from the outer layer of the organic basis of the prismatic sub-
stance (text-fig. 35, p. 302; see also Pl. XXXIV. fig. 6). Here
marginal growth proceeds by a series of steps and retreats, the free
mantle-margin being retractile to the edge of the nacre, and being
so retracted when the shell closes. Thus, after a new process
of the lip has been formed, the mantle-margin is withdrawn,
and forms a fresh attachment on the inner surface of the last-
formed lip, from which a fresh lip is produced. So the periostracum
of lip no. 2 is attached to and apparently a direct continuation of
the inner surface of the conchyolin of the prismatic layer of lip
no. 1, and constitutes the outer layer of the conchyolin of the
prismatic layer of lip no. 2. But Herdman has shown that,
difficult. as it is to distinguish a separate periostracum in sections
of the shell, such a layer, of extreme delicacy, does exist at the
[43]
302 DR. H. LYSTER JAMESON ON
margin, and arises in the normal manner in a marginal groove
(Ceylon Report, Part If. Anatomy of Pearl-Oyster, plate vin.
fig. 2
Text-fig. 35.
ANINTatt ;
Marga ritifera vulgaris, Persian Gulf. Section through the lip of the shell, after
decalcification, showing the successive lappet-like processes of the prismatic
substance (2.,7./, 1.7, 0./’’). pr. prismatic substance ; Sév., stratification of same.
iA AS, A’, A’”’, points marking the successive retreats of the secreting margin,
which takes place when new lappets are to be formed. At these points the
‘ periostracum ” of the new lappet is continuous with, and indistinguishable
from, the inner conchyolin-layer of the prismatic substance of the last-formed
lappet. Preparation X (xX 35), see also Pl. XXXIV. fig. 6
(ii.) Zhe Prismatic Substance.
Reduced to its simplest terms the prismatic layer of the
Mother-of-Pearl shell consists of prisms of calcium carbonate
perpendicular to the surface of the shell, bounded externally and
internally by membranes of conchyolin, which are connected by
vertical membranes forming the septa between the prisms
(text-figs. 35 and 36; see also Pl. XXXIV. figs. 6, 6a; Pl. XL.
fig. 29a). Where interruptions in the continuity of the growth
of this layer have occurred, the layer of prisms may be divided
by one or more horizontal walls of conchyolin (text-figs. 35, str.,
and 38, str.), which break up the prisms into segments, or which
divide the layer into two or more series of prisms. The individual
ends of the prisms in one layer do not of necessity coincide with
those of the prisms in the next layer, though they frequently do
coincide. The septa between the prisms may also show annular
thickenings, corresponding to zones of constriction around the
prisms (Pl. RK LY. fig. 6 a,ann.). Romer has shown (82, p. 35)
that the prisms of the pearl- -shell (like those of Pinna, described
by Biedermann (1), p. 9) behave between crossed nicols in the
same manner as single crystals. The prisms differ enormously in
size, according to the age of the oyster and the conditions under
which they are secreted.
There is a sharp line of demarcation between the prismatic
and the nacreous layers in Margaritifera, the innermost layer of
the conchyolin of the former being connected to the outermost
layer of that of the latter by a series of fine connectives of
conchyolin (Pl. XXXTV. fig. 6 a, con.), forming a curious alveolar
layer.
[44]
THE CEYLON PEARL-OYSTER. 303
The prismatic substance is secreted by that part of the epidermis
apposed to the inner surface of the shell which is nearest to the
margin of the mantle, and it is clear from the rapidity with
which the columnar lip and its lappet-like processes are re-
generated when injured and are added to in growing young shells
that the characters of this layer are associated with relatively
rapid secretion. This is significant, in view of the resemblance
of this layer to some of the rapidly secreted repair-substances
which replace the nacre under certain abnormal conditions
(see below).
Romer’s work (p. 18) gives an interpretation of the nature of
the prisms, which | have found most useful in helping me to
interpret my own observations on pearl-formation. According to
this hypothesis, which was suggested to Romer by my illustrious
teacher, Prof. Biitschli, each prism is an incomplete spherocrystal,
the growth of which has been arrested in all directions but one,
viz. the direction from which the new shell-substance is secreted.
Romer says (p. 18) :—
“Dass diese Spharokristalle der einzelnen Prismen so
unvollstindig ausgebildet sind, rithrt daher, dass gleichzeitig
und dicht nebeneinander die Anfiinge der einzelnen Prismen
oder. Spirokristalle gebildet wurden, die bald seitlich
aufeinander stiessen und sich so gegenseitig in der weiteren
Ausbildung hemmten ; nur an ihren inneren’ Enden
vermochten sie einseitig weiter zu wachsen ” *,
If I may be allowed to state the proposition in shghtly
different terms, the prismatic shell-substance (and, indeed, if my
interpretation of the variations of the nacre, normal and patho-
logical, are correct, the whole of the shell-substance) agrees with
a spherocrystal in that it is composed of crystalline or crystallised
substance which can only grow by the apposition of fresh layers
deposited on a single surface, owing to the matter in solution
only having access to one surface of the crystalline mass. When
this surface is the outer surface of a sphere, a body with more or
less of the characters of a spherocrystal results (e. g. Harting’s
bodies and Pearls); where it is approximately a plane surface, as
in the growth of the Molluscan shell, a structure such as the
* Bitschli in 1908 (6, p. 26) explained his definition of ““ spheerocrystals,’’ more
especially with reference to the crystal-like prisms of Pinna (and by analogy
of Margaritifera), as follows :—
“Wie aus den Darlegungen in meinem Werk von 1898 hervorgeht, verstehe
ich unter einen solchen nicht ein Aggregat zentrisch angeordneter Kristallnadeln
oder Einzelkristalle, was zwar die tibliche Anschauung ist, sondern ein
einheitliches Kristallgebilde, in welchem die besonderen feinsten Struktur-
verhaltnisse, die auch den gew6hnlichen Kristallen ihre charakteristichen
Kigenschaften verleihen, nicht entsprechend einer Axe, sondern um ein Zentrum
radiar orientiert sind. Wenn daher der Radius eines solchen Spharokristalls
sehr gross wird, und man ein radiales Stiick desselben, weit entfernt von dem
Zentrum, herausschneidet—und so verhalten sich etwa die Pinnaprismen—so
muss dieses Stiick sich natiirlich wie ein gewodhnlicher Kristal verhalten ;
obgleich die von mir gegebene Zuriickfiihrung auf einen Sphiarokristall mit
erossem Radius ganz zutreffend ist.”
[45]
304 DR. H. LYSTER JAMESON ON
Molluscan shell results, the axes of its constituent elements being
approximately parallel.
(iu1.) The Nacre.
This substance, which forms the bulk of the shell, and gives
the shells of the genus Margaritifera their commercial value as
Mother-of-Pearl, and the pearls their beauty, is stratified, and
in it the calcium carbonate is divided into extremely minute
bodies in the organic network. It is secreted by the outer surface
of the mantle and body-wall.
I will not attempt here to review the many writings on the
structure of this layer. J can at present add little to the recent
work of Romer (32), who has studied its structure and that of its
decalcified conchyolin framework very thoroughly. The organic
basis which gives it its form, and which retains its iridescence
after the calcareous salts have been extracted, consists of a series
of parallel lamelle, of extreme fineness, united to one another
at intervals by radial connections, so as to form a series of minute
flat or lenticular chambers, separated by organic walls of extreme
delicacy. The calcium carbonate appears to be enclosed in
these chambers in the form of little polygonal plates or lozenges.
This structure is difticult to observe, owing to the distorting
effect of the decalcification process, which, owing to the evolution
of gas-bubbles, tears some lamelle apart and forces others
tightly together. It becomes much more obvious in some of
the abnormal and pathological varieties of nacre described as
“repair-substance ” below, notably in ‘ granular repair-nacre.”
I believe that the lustre (not the iridescence) of mother-of-pearl,
and of pearls, is in great measure due to the fact that each of
these tiny plates is a minute, biconvex lens; and that the
extraordinary and indescribable character of the light reflected
from the surtace of a fine pearl is in part the cumulative expression
of the action of these myriads of little lenses upon the light
reflected from the surfaces of calcium carbonate and of conchyolin
which underlie them.
(iv.) Hypostracum, or Muscle-Attachment Substance.
This curious substance has not secured all the attention it
deserves. It has been described by several writers under the
names Hypostracum (Thiele, 46), Stiibchenschicht (F. Miiller,
29), durchsichtige Substanz (Ehrenbaum, 9; Tullberg, 47).
T retain the name hypostracum, as emphasizing the distinct
origin and characters of this layer, and as shorter and more
convenient than ‘‘durchsichtige Substanz.”
This hypostracum is a fine columnar layer forming the surfaces
where the muscles are inserted into the shell (Pl. XXXIV. figs. 5
& 7, hy.; text-figs. 36 & 37).
It is more transparent than the nacre—indeed, the iridescence
and lustre of the muscle-sear is due to the nacre lying below and
[46]
THE CEYLON PEARL-OYSTER. 305
shining through this ‘“ durchsichtige Substanz,” the substance
itself not possessing the structure to which these optical properties
are due.
It is composed of columnar or fibroerystalline needles of
carbonate of lime (Stiibchenschicht, Miiller), but shows in
places, in addition to its columnar structure, a distinct strati-
fication parallel to the surface; this is seen also in the basis
which remains on decalcification (Pl. XXXIV. fig. 5). I attri-
bute this stratification to variations in the organic basis, which
are probably independent of the form and structure of the
crystalline needles. Hypostracum only oceurs where the
specialised muscle-attachment epithelium is inserted into the
shell, and, as the muscles move away from the umbonal region
with the growth of the shell, it is quickly covered over by ordinary
nacre which is deposited in the wake of the advancing muscle.
In a section of the shell from the umbo through the adductor
scar the hypostracum layer can be traced across the shell through
the nacre from the scar to the umbo, the thickness of the over-
lying nacre increasing as the umbo is approached, By means of
this hypostracum layer, the wandering of the adductor muscle is
recorded in the shell-substance (text-fig. 36, hy.),
Text-fig, 36.
Margaritifera maxima Jameson. A young shell or “chicken shell”? from Port
Darwin, Northern Territory of Australia (London markets). Section from
the umbo to the shell-margin passing through the middle of the adductor
impression, pr., prismatic layer; A—B, muscle-scar, covered with “ Hypo-
stracam”; hy., the hypostracum layer, by means of which the migration of
the muscle, from what is now the umbonal region, with the growth of the
shell can be traced; nac., nacre of the shell-margin, formed external to the
muscle-sear; nac.’, nacre of the thick subumbonal region, deposited internally
to the hypostracum, ‘I'wo-thirds of natural size.
In the shell figured, a young example of the large white
Australian Mother-of-Pearl shell (Jf. maxima Jameson), the
hypostracum is 18-20 « thick over the muscle-scar, thinning
out to 10» and then to 4 or 5 w at the extreme outer edge of
the scar, where the muscle has most recently made attachment.
As this layer is traced backwards towards the umbo, through the
nacre, it is found to get gradually thinner, just as the prismatic
substance (which in this shell is about 1 mm. thick in the region
of the adductor scar, and in the lip of very old examples of the
same species may be 2 or 3 mm. in thickness) is found to get
thinner towards the umbonal region, These differences are no
doubt associated with the relative ages and sizes of the animal at
Proc. Zoou. Soc.—1912, No. XX. 20
[47]
306 DR. H. LYSTER JAMESON ON
the respective periods, and with the relative rapidity of peri-
pheral growth in young and older oysters. Text-fig. 87 shows the
hy postracum of the same example (J/. maxima) enlarged torty
times.
Text-fig. 37.
STATA NTT
The inner limit of the adductor sear, in the same shell as that shown in text-fig. 36.
hy., hypostracum; nae., nacre external to same; nac.’, nacre internal to
same. X 40.
Exactly the same relations occur in J/. vulgaris, a section
through the umbonal side of the adductor sear of which is shown
in Pl. XXXIV. fig. 7. But in this example, an old thick Lingah
shell from the Pen Gulf, in which, in all probability, peri-
pheral growth, and consequently the wandering of the muscle,
had ceased, the hypostracum is thicker, measuring 130 « in
thickness.
The hypostracum undergoes but little secondary thickening,
compared with the nacre. Hence, in thick massive shells like
M. maxima, where the newly forming nacre in the umbonal
region and also towards the lip and around the muscle-sear out-
strips the hypostracum in development, the muscle-scar is the
thinnest part of the entire shell, except the extreme edge. This
is well seen in text-fig. 56, in Pnich figure the area between A
and B represents the muscle- impression, but it is even more
obvious in older thicker shells. Some interstratification of
hypostracum and nacre occurs at the borders of the muscle-scars,
where changes in the outline of the muscle have taken place.
This is ficured by Tullberg in Mytilus (47, Taf. v. fig. 2). The same
is Shown for Margar itifera vulgaris at hy.', hy.", in Pl. XXXIV:
fic, 7. Felix Miiller (29, Taf. xxix. fig. 13) shows the lateral
transition of this substance into nacre. I have observed the
same thing in some of the ‘ Muscle-Pearls” described below.
When decalcified the hypostracum leaves behind it an organic
basis, which is somewhat different from the conchyolin of the
rest of the shell in its reaction towards stains. his is of interest
in connection with the view generally held that this layer,
unlike the other calcareous parts of the shell, which are probably
(48)
THE CEYLON PEARL-~OYSTER. 307
due to simple secretion, arises by a gradual transformation into
shell-substance of the outer regions of the specialised epidermal
cells which underlie it, 7, e. in the same manner as the Crustacean
carapace and the outermost layer of the periostracum. It shows
a well-marked striation perpendicular to the surface, the striz
no doubt corresponding to the outlines of the spaces which were
occupied by the needle-like fibrocrystalline bodies of calcium
carbonate, and also at times indistinct lines parallel to the surface
(Pl. XXXIV. fig. 5). In sections in the plane parallel to the
surface this substance shows an alveolar structure. It sometimes
shows a tendency to break up into segments, corresponding to
the underlying epithelium-cells (Pl. XXXIV. fig. 5, hy.’).
(v.) Hinge-Ligument.
I do not propose to discuss the hinge-ligament here, as it has
not the same direct bearing on the question of pearl-formation
as the above layers, though leathery pearls, composed of this
substance, are sometimes found (e. g. in JZ. maxima in Australia).
(10) Tae SHELL-secretinG Eprruecia.
The ordinary shell-secreting epidermis of J/. vulgaris, so far
as I have been able to study it in the unsatisfactory material
available, consists of columnar or tesselated cells (Pl. XXXY.
firs 8 eps; te 29. 0;ep; 5. Pin XX RV I. firs D1y.06p.5cPl.,, SLM.
fig. 33, ep.), brick-shaped or palisade- like, according to the
degree of contraction, in sections perpendicular to the surface,
with a certain and variable number of goblet- and gland-cells.
The nuclei of the epidermal cells are oval or spindle-shaped.
These cells are attached to the subjacent tissues by a basement-
membrane of delicate fibrille which distinctly marks the
boundary between the epidermal epithelium and the subjacent
tissues. Beneath this epidermis is a characteristic granular
parenchyma (Pl. XX XV. figs. 8&9; Pl. XXXVI. figs. 10 & 11;
Pi ee eV AL fig, 145, Pl. ane fig. 33, par.), which contains a
great variety of elements, some being comparable to the
‘* Rundzellen” and ‘ Langer’schen Blasen” described by List
(27 b) for the Mytilide, some being dark-staining, apparently
glandular elements that open out between the epithelial cells
(fig. 33, gl.). As observed by List (276), this epithelium and the
underlying tissues are excessively variable in their characters.
Over the surface of the muscle-attachment the epidermis is
different (Pl. XX XIII. figs. 4, 4a@; Pl. XXXV. fig. 8, m-ep.).
Here it consists of columnar cells, usually about 10-12 p» long
and 2-4 » broad, which pass over basally without any distinct
dividing-line into the muscle-fibres. Whether the transition
is direct, or whether in fact a connective-tissue junction is
present, cannot be determined from the available preparations
of Margaritifera vulgaris; but in Mytilus edulis there is a
distinct connective-tissue layer (fig. 5, ¢.¢.), the fibres of which,
20*
[49}
308 DR. H. LYSTER JAMESON ON
continuous with the bases of the epidermal cells, are attached to
the ends of the muscle-fibres (mzse.), which may be produced out
into tails. Tullberg recognised that such a junction was present.
In Margaritifera vulgaris the attachment epithelium-cells may
have one or several tails, probably also of connective-tissue
character, passing over into as many muscle-fibres.
Distally these epidermal cells broaden out somewhat, ending
in a clean-cut surface, which may be represented in section by
a clear zone forming a slightly acute angle with the sides. The
nuclei, which are oval and about 3-4 uw long, are situated in
the middle of their length.
It is possible to make out, in some cases, a striation of these
cells in the direction of their long axes. Occasionally the distal
surface is raised into processes and papilla, but this may well
be a result of imperfect fixation of the tissues.
These cells stand out as stiff, independent, almost bristle-like
entities, and are probably hard and tendinous in character,
They are frequently preserved in old preparations in which
all traces of the structure of the ordinary epithelia have
disappeared. In some cases they seem to have been drawn out
in the fixing process ; thus the longest cell shown in Pl. XX XIIT.
fig. 4a measured 26 4. It seems possible that in the shrinkage
consequent upon fixation the majority of the elements here
had broken away from the shell, but that this particular cell
had remained attached and was consequently fixed in a state
of extension. ‘This figure shows that the connective-tissue
elements extend up between the bases of these cells.
This epidermis is very closely adherent to the specialised shell-
layer (hypostracum) to which it is attached, and the connection
seems to be between the cells and the organic basis of the shell.
Thus, in decaleifying a piece of the shell of J/ytilus with the
adductor muscle attached, the hypostracum remained adherent
to the epithelium and tore away from the rest of the shell
CP]; SOXER Ve hie 75))
(11) SHett-SEcrerIoN.
I will not attempt to survey the writings of previous inves-
tigators on this subject. This has been ably done by Stempell
(45), whose review contains a full and lucid discussion of the
question.
The general trend of opinion now seems to favour the theory
dating back to Reaumer, 1709 (31), and held by Tullberg,
Ehrenbaum, Moynier de Villepoix, and the majority of recent
French and German investigators, that the shell (except the
outermost layer of the periostracum and the hypostracum) is
formed from a fluid secretion, rather than the theory specially
associated with Huxley’s name (24) that the shell is derived
from a succession of fully developed skins or cuticles, shed as
membranes by the underlying epidermis.
[50]
THE CEYLON PEARL-OYSTER. 309
The outermost layer of the periostracum (which in Margariti-
Jera is a negligible quantity) and the hypostracum probably
arise by direct transformation of the outermost portions of
specialised epidermal cells, and on this account it may prove
necessary to draw a sharper morphological distinction between
them and the rest of the shell than has hitherto been done *.
The prismatic layer and the nacre, together with the inner
layers of the periostracum, more probably arise as a secretion
which first hardens into a membrane in sitw, and then forms
the delicate skin which Huxley observed between the mantle
and the shell in the freshwater mussels.
It would appear that the lime-salts and albuminous fluid
which hardens to form the conchyolin are independent of each
other, and may be secreted in varying proportions. Where
these two constituents are secreted under circumstances which
inhibit the control of the shell-secreting epidermis, or where
the secretion takes place so copiously and rapidly that the
epidermis is unable to regulate the deposition (as in the patho-
logical cases described below), lime-salts are precipitated in a
columnar form, much as in Harting’s bodies, and, concurrently
with this, the albuminous fluid is transformed into an insoluble
substance resembling conchyolin. The process of shell-secretion
at the rapidly growing edge of the shell resulting in the
formation of the prismatic layer—which in Margaritifera
vulgaris measures aS much as 1 mm. or more in thickness—is
probably in some degree analogous to the process of secretion of
repair-substance, the epithelium exercising comparatively little
control over the arrangement of the elements.
But in the case of the nacre it is different. Here the epithe-
lium seems to exert a definite and very strict selective influence
resulting in the finely stratified and chambered structure which
can, I think, best be interpreted as arising from rhythmically
intermittent secretory action on the part of the controlling
epidermis. Any disturbance of the normal rhythm of this
secretion, e.g. the stimulation of an intrusive particle between
shell and epidermis, results in the formation of the irregular
substances described below, such as granular repair-nacre, the
several varieties of columnar repair-substance, or the amorphous
non-calcified substance.
It would thus seem as though the structure of the shell-
substance, and its variations, normal and pathological, could
be expressed in terms of the proportions of lime-salts and organic
* The difference between the outermost layer of the periostracum and the hypo-
stracum on the one hand, and the remainder of the shell on the other, the former parts
arising by direct cell-transformation or cuticularisation of cell-protoplasm, the latter
as a secretion poured out by the cells, suggests a line of inquiry that might yield
interesting results. Can these two constituents of the shell be separated morpho-
logically and phylogenetically, and, if so, can the former be regarded as in any sense
homologous with the cuticular exoskeleton of an ancestor common to Mollusca and
Arthropoda, the latter being a subsequent addition peculiar to the Mollusea.
associated with their more sedentary modes of life, which has now, for all practical
purposes, replaced the more strictly cuticular element as an exoskeleton ?
$10 DR. Il. LYSTER JAMESON ON
salts secreted and of the periodicity of the secretion as determined
by the control, or loss of control, of the secreting epidermis.
In fact, if my interpretation is correct, the processes involved
in the building of the shell ave the usual chemico-physical ones
which govern erystallisation in colloidal media * controlled and
limited by the time-factor which is a function of the activity
of the living cells.
It is less easy to imagine the conditions which determine
the transformation of the fluid albuminous secretion into the
leathery conchyolin. One is naturally tempted to postulate
a chemical transformation asa direct or indirect result of the
action of nascent CaCO,, as in the case of the calcoglobin in
Harting’s bodies (12); "put the formation of this substance
apart from the lime-salts, e.g. in the inner layers of the perio-
stracum and in amorphous repair-substance, and in the case
of shells grown in lime-free media (Moynier de Villepoix, 28,
p- 122), seems to negative this; and it may well be that ap
change to an arial ble albuminoid is directly brought about
by the action of the secreting cells themselves, or follows from
the chemical composition of the secretion as shed.
(12) ABNORMAL AND PaTnoLoGIcAL PHASES OF THE
SHELL-SUBSTANCE.
For a study of the beginnings of Ceylon pearls, a consideration
of the variations in the shell-substance, when it is secreted
under abnormal conditions, either on the surface of the shell
or of a growing pearl, is of importance.
Where the normal rhythm of the process of shell-secretion is
interrupted, e.g. by injury to the shell, or the intrusion between
the epithelium and the nacre of a foreign particle or by other
disturbances less easy to explain, certain irregularities in the
process of secretion occur, resulting in an alter ed product.
In the simplest case such a disturbance results in a modification
producing a granular appearance of the conchyolin-layers of
the nacre. This modified substance I propose to ‘eal “ granular
repair-nacre.” In sections made through this substance, after
decalcification, the normal stratification is obscured by a highly
granular appearance which seems to be due to an infinite
number of connections between the successive conchyolin-layers
resulting in a distinctly alveolar membrane. This is shown
in text- fig. 38 (repnac.), which is taken from an artificial
“plister ” produced by the writer in Margaritifera margaritifera
after the “ Linneus” method, in British New Guinea in 1899.
The foreign body was inserted near the mantle-margin, and the
mantle secreted first a double layer of the prismatic subtance,
* Biedermann (2), p. 171, recognises that the structure of the shell is essentially
reducible to crystallisation processes, the influence of the cells being limited to the
composition of the fluid, and perhaps the orientation of the primary centres of
crystallisation. But I would add to these influences the periodicity of their
action.
[52]
«
THE CEYLON PEARL-OYSTER. ale
and then nacre, which, at places, showed the characters of
“ sranular repair-nacre,”
Text-fig. 38.
Margaritifera margaritifera Linneus (Black-lipped Mother-of-Pearl Oyster).
Part of an artificially produced blister. pr, prismatic layer ; Sér., horizontal
dividing membrane of conchyolin in same; nae., nacre; rep.nac., granular
repair-nacre. (Preparation VIII.)
Pl. XL. fig. 29, from the “repair-membrane” formed by
M. vulgaris over a hole in the shell (umbonal region), shows the
same substance at é7.' passing over on the one hand into columnar
repair-substance, on the other into nacre. The same substance
is seen at dr.
Pl. XLI. fig. 30 (rep.nac.) shows the same substance, secreted
at the point of junction of two pearls (from one of Dr. Kelaart’s
specimens of JZ, vulgaris). Here it was secreted as a result
of disturbances following upon the fusion of the two pearls and
the absorption or calcification of the intervening tissues. ‘The
granular repair-nacre in the preparation shows in places a
distinetly columnar structure, indicating a transition to the
columnar repair-substance ; such a transition is still more obvious
in Pl. XL. fig. 29.
The same granular repair-nacre is seen in Pl. XXXYV. fig. 9,
Pl. XXXVIL. fig. 15, and Pl. XX XVIII. fig. 18, surrounding the
central cavities of ‘ muscle-pearls,” where unduly rapid secretion
might well be expected, and in Pl. XX XIX. fig. 23, where a
hypostracum-pearl (‘“ calcospherule,” Herdman) is in process
[53]
ty
—
lo
DR. H. LYSTER JAMESON ON
of being coated over with nacre. The same substance is well
shown in Pl. XLI. fig. 35 and Pl. XLITI. fig. 43 (gr.). In the
last-named case if is seen to pass over on the one hand into
nacre, on the other into columnar and amorphous repair-
substances.
The next form of repair-substance is much more variable,
and occurs in several distinct, though intergrading forms. I
propose to call this “columnar repair-substance,” in view of the
calcium carbonate being crystallised in columns.
Columnar substance resembles, more or less, the prismatic
layer of the shell—indeed, it is probable that Rubbel (33, p. 171)
had. a substance analogous to this columnar substance before
him when he stated that the outer epithelium of the mantle
of Margaritana is capable, in repairing the shell, of producing
the prismatic substance which is normally only the product of
the mantle-margin. (In the same way, he treats as ‘“ peri-
ostracum” the non-calcified material secreted under similar
conditions, which I describe below as ‘amorphous repair-
substance ”’.) *
In its simplest form columnar repair-substance consists of
parallel needle-like reds of carbonate of lime (which Steinmann
(43), speaking of Harting’s bodies, has aptly called “ fibro-
crystalline ”) deposited in an organic conchyolin-matrix, which,
when the caleium carbonate is removed by acids, and a section is
cut at right angles to the surface, presents a palisade-like appear-
ance, due to the septa of conchyolin between the calcareous rods
(Pl. XL. fig. 29; Pl. XLI. fig. 30, col.). In horizontal section
this conchyolin has a honeycomb-like structure.
All kinds of variations occur in the coarseness or fineness
of the calcareous elements and the organic framework.
This substance is frequently formed on the surface of the
shell or of a pearl when disturbances arise in the rhythm of shell-
secretion. In Pl. XL. fig. 29 it is seen in the repair-membrane
formed over an injury caused to the shell by a boring parasite.
In Pl. XLI. fig. 30 it is seen (col.) in the angle between the
surfaces of two pearls which have become secondarily attached
together.
Pl. XLI. fig. 31 shows the same substance developed under
conditions similar to those existing in fig. 30. This figure is
a drawing of a section through the suture between two pearls
which have become secondarily fused together. The pearls
themselves, with the intervening suture, are elton moan! 1] eXelnive
fig. 49; the end of the suture, where the curvatures of the two
pearls diverge, in fig. 31. In the entire object, examined in
oil of cloves ‘(fig. 49), the suture was represented by a yellowish-
brown line, the colour being due to the dead remains of the
cellular membrane which originally separated the two pearls.
* While these substances are perhaps not strictly separable respectively on
chemical and physiological grounds, I think it is well on morphological and patho-
logical grounds to emphasize the distinction.
4]
THE CEYLON PEARL-OYSTER. 313
The membrane consisted of the lining epithelia of the two sacs,
and a layer of parenchymatous tissue between these two
epithelia.
The epithelia, and even the individual cells of the parenchyma,
can be detected in some places (Pl. XLI. fig. 32).
If we try to trace the steps resulting in the condition figured
on Pl. XLIV. fig. 49 and on Pl. XLI. fig. 31 (¢.e. to survey the
story of the formation of a double pearl), we may assume that
they were as follows. As the two neighbouring pearls, each
enclosed in a sac, grew in size, by the addition of fresh layers,
they exerted a pressure on the intervening tissues, resulting in
reduced circulation and consequent malnutrition which began
at the first point of contact and extended outwards. Thus the
contiguous surfaces tended to become flattened (fig. 49), and the
intervening tissue, consisting of the epithelia of the two pearl-
sacs and a small amount of connective-tissue between them,
finally ceased to be functional, died, and was preserved as a
yellow membrane (P]. XLI. fig. 52). At the periphery of the
area of contact, where the curvatures of the two pearls diverged
and were separated by a wedge-shaped plug of tissue, nacre-
secretion continued longer, the last efforts of the epithelia
being represented by mac. and wae.’ in fig. 31. Finally, the
epithelium ceased to control the deposition of its secretion, and,
with the shrinkage of the atrophied tissues a space occurred
on each side between the nacre and the epithelium, into which
an extravasation of organic matter and salts occurred. The
salts precipitated themselves in the form of columns or raphides
with their bases apparently in or on the epithelia, and con-
currently with this precipitation the soluble organic substance
became converted into the conchyolin framework between the
prisms, analogous to the ‘ calcoglobin ” framework of Harting’s
bodies, derived from egg-albumen when calcium carbonate is
precipitated in it. Lastly, the epithelia and intervening con-
nective-tissue died and probably underwent irregular calcification,
breaking away from the still functional tissues and becoming
incorporated in the substance of the pearl. The still functional
tissues now formed a single sac surrounding the two pearls, and
quickly enveloped them both in a common nacreous covering.
Similar processes can be postulated to account for the condition
shown in Pl. XLI. fig. 30. Here, between the curvatures of the
surfaces of the two contiguous pearls, there was a triangular
plug of tissue, which for some time remained attached to the
degenerated membrane which separated the pearls. Its epithe-
lium gave rise before it broke away to granular repair-nacre
(rep.nac.) on the right, where the disturbance was presumably
least, and to a small amount of columnar repair-substance (col.)
on the left. Then it broke away from the degenerated and dead
membrane between the pearls and retreated rapidly, exuding
as ib went the albuminous fluid, which, being secreted at a much
greater rate than the lime-salts, was practically devoid of lime
[55!
314 DR. H. LYSTER JAMESON ON
and formed coarsely stratified amorphous substance (am.), broken
by cleft-like cavities. Later on, when the retreat of the plug
of tissue was less rapid, this amorphous substance passed over
into columnar substance (é.) and granular repair-nacre (¢r.'), and
finally gave place to the nacre (nac.’) of the common investment
of the compound pearl.
The columnar repair-substance varies enormously, and passes
over imperceptibly into “amorphous substance” or lime-free
conchyolin, granular repair-nacre, ordinary nacre, and the
prismatic substance of the shell. For example, the repair-
membrane, a part of which is shown in Pl. XL. fig. 29, showed
an immense number of variations from place to place. In some
parts a second layer of amorphous substance was interpolated
between the columnar layers; in others the columnar substance
passed over into a coarsely alveolar substance with irregular
cavities, some of which penetrated into the amorphous substance.
In yet other spots the amorphous substance passed over through
granular repair-substance into nacre.
Columnar substance is frequently stratified, consisting of a
number of consecutive layers. This is seen at col.’ in the repair-
membrane figured at fig. 29. It is also shown in the pseudo-
nucleus of the pearl shown on Pl. XL. fig. 28 and Pl. XLIV.
fig. 49, and in the pearls from the Persian Gulf in Pl. XLI.
figs. 33 & 34, In the former of these last-named instances it
occurs immediately around the central cavity, in the latter case
interstratified and intergrading with the nacre.
Im Pl. XOLIID. fig, 43 *(col.) it is seen passing over on the one
hand into granular repair-nacre, on the other into amorphous
repair-substance. ‘The same stratified columnar substance is well
shown in Pl. XLV. fig. 51, where it forms a curious flaw running
through the substance of a pearl.
Apart from this direct stratification, the columnar repair-
substance may have an internal alveolar structure such as is
shown in Pl, XLII. figs. 36, 37, & 38. Figs. 40-42 on the same
Plate, taken from the pearl shown in Pl. XLVI. fig. 57 (a brown
pearl composed of prismatic shell-substance), show the transition
from amorphous repair-substance to columnar repair-substance
(figs. 41, 42, col.), and from the latter to the prismatic layer of
the shell (fig. 42, pr.).
The third variety of repair-substance I call amorphous repair-
substance. In its typical form this substance is seen at am. in
Pl. XL. fig. 29, where it is obviously the result of the first effort
of the mollusc to close the injury to the shell, and in Pl. XLI.
fig. 30, where it is the product of a fully functional epithelium,
retreating rapidly and leaving its secretion in its wake. It shows
little or no structure under ordinary magnifications, but is usually
faintly stratified. Jt may contain cavities, arranged in rows
parallel to the secreting-surface, and with at times also a radial
arrangement. ‘These cavities typically contain carbonate of lime.
Pl. XL. fig. 29 @ (Margaritifera vulgaris, Lingah Shell, Persian
[56 |
THE CEYLON PEARL-OYSTER, 515
Gulf) shows this substance formed as the first step in the
development of a new layer of prismatic substance to cover over
the tube of the worm Leucodore, which has entered between the
mantle-margin and the shell, as is its wont. Here the mantle-
margin, reacting to the stimulation of the parasite, has retreated
and secreted a new “lip” to exclude it. This lip, like the
normal lip, consists of the prismatic layer of the shell, but
the irregularly secreted first layers of it consist of amorphous
substance, containing alveoli in which a scanty supply of calcium
carbonate was deposited.
The amorphous substance frequently occurs in the centres
and around the central cavities of pearls, where it doubtless
represents the first matter which the molluse shed into the cavity.
It probably corresponds to the ‘“ Theile des Schalenepidermis ”
recognised by von Hessling (18, p. 313) in the nuclei of
pearls, and the ‘“ Kern von Chitinsubstanz” referred to by
Pagenstecher (30, p. 502), and perhaps to the ‘“ Gelbbrauner
Substanz” of Rubbel (34, p. 412).
The amorphous substance shows little receptivity to stains.
It passes over sometimes into columnar substance (Pl. XLI.
fig. 30, é.), sometimes into granular repair-substance (Pl. XL.
fig. 29, t., tr.'; Pl. XLI. fig. 30, ¢r.'). It also sometimes inter-
grades with a substance resembling the prismatic layer (Pl. XLII.
fig. 41). Similar intergradations with prismatic substance were
shown in some parts of the preparation from which Pl. XL.
fig. 29a is drawn. Pl. XLII. figs. 40-42 are of interest as
showing all manners of intergradations between amorphous,
columnar, and prismatic substances, the different structures
shown being apparently mainly dependent upon the proportions
of calcium carbonate present. Thus we have in this pearl,
which, owing to the impermeability of the amorphous substance,
was imperfectly decalcified, tracing the layers from inside out-
wards: (1) a plug of nuclear matter of doubtful origin con-
taining well-marked crystals (fig. 40, ma.)—these are true
crystals (rhombohedra) ; (2) a ‘layer of amorphous substance,
passing over into typical simple columnar repair-substance (fig.
40, col.); (3) numerous layers of amorphous substance (figs. 40,
41, am.), some layers being quite lime-free, some having scattered
alveoli containing calcium carbonate, some showing their cavities
in radial rows, leading up, by transitions, to regular columnar
substance (figs. 41, 42, col.), which differs from the prismatic
substance proper (fie. 42, pr.) only in the smaller diameters
of its constituent elements, a difference which, in view of the
variability of the sizes of the prisms in the shell itself, is com-
paratively unimportant.
Again, the transition from the abnormal repair-substances to
nacre in the pearl shown in Pl. XLV. fig. 52, col., and Pl. XLII.
ne. 36, col., is equally striking. This is shown in detail in
aman fig. 43. At mu. is the outer wall of the sphero-
Pelee or columnar pseudo-nucleus of the pearl. At nac. is
[57]
316 DR. H. LYSTER JAMESON ON
shown the normal nacre of the pearl. The first-formed layers of
nacre are incomplete, passing over into this area of repair-
substance, and all stages of transition may be seen, corresponding
to the gradually increasing control exercised by the secreting
epithelium.
At first, amorphous substance (am.), alveolar in places, was
secreted, no doubt with irregular crystallised bodies in the alveoli,
some of which are actually preserved in the preparation, owing
to incomplete decalcification. Peripherally this gave place to
columnar substance (col.), which acquired a finely alveolar structure,
and passed over, through granular repair-nacre (g7.), Into normal
nacre (nac.'), the layers of the conchyolin of which gradually merge
into the horizontal markings of the granular substance. The
amorphous substance in this preparation varies from layer to
layer in the degree to which it is alveolar ; at some places it
might better be described as coarsely columnar substance.
Amorphous substance seems to be the first product where the
shell is perforated and the mantle makes a sudden effort to close
an opening to the exterior. In such cases it may be secreted so
copiously that a tough leathery skin results, with little or no lime-
salts in it (Pl. XL. fig.29, am.). It is hkewise secreted in layers
when a break occurs in the nacre-secretion of a pearl or of the
shell, owing to a pathological extravasation of cellular matter
(Pl. XX XVIII. fig. 17, am., am.’). These facts suggest that the
organic basis of the shell is the constituent the secretion of which
varies in quantity, the secreting-tissues (perhaps the granular
subepithelial parenchyma in Margaritifera) containing a
reserve of this material which can be poured out profusely when
the shell is injured. It would seem that the lime-salts, on the
other hand, are secreted more regularly, so that the mechanism
for furnishing these cannot keep pace with that which yields the
organic substance when the latter is called upon to make a
special effort to repair damage. The resemblance of the inner
layers of the periostracum (in forms with a thick periostracum)
to amorphous repair-substance may perhaps be explained by
postulating the absence or inhibition of the lime-secreting
mechanism in the underlying tissues.
That the secretion of calcium carbonate could not keep pace
with that of the organic substance, when the latter is produced
in large quantities, is easy to understand in view of the very
small proportion of CaO in the blood of Mollusca, and indeed of
all invertebrates that have been investigated. According to
Griffiths (quoted by Biitschli, 6, p. 62), the CaO in the blood of
a number of bivalves examined varied from 0°032 per cent. in
Anodonta to 0:067 per cent. in Mytilus.
Amorphous substance is seen in the pseudo-nuclei of pearls in
P). XX XIX. figs. 20 & 21, and Pl. XL. figs. 24, 26, & 27; figs. 20,
24, & 27 showing particularly well its continuity and intergra-
dation with the organic basis of the columnar repair-substance.
In the centre of a pearl it may contain, in addition to the
[58]
THE CEYLON PEARL-OYSTER. BIL
central cavity, secondary cavities in its substance, in which
organic particles are lodged (fig. 20).
The variations of coarsely alveolar structure which amorphous
substance shows (e.g. Pl. XL. fig. 29 a@ and Pl. XLII. figs. 40 & 41)
recall those structures which Biitschli (6, Taf. iii. figg. 20-33)
describes in the spherocrystals of (?) Trydimite formed when the
siliceous concretionary substance of the Bamboo (known as Tabaxir
or Tabasheer) is heated ; this structure is probably in great measure
the expression of the physical conditions (surface tension, etc.)
which prevail when two substances in solution or in a colloidal
state separate from one another to form a spherocrystalline
mass.
Pl. XLII. figs. 37 & 39 are of interest as showing another
variation of the nacre, in the direction of columnar substance.
In this variety of nacre, the conchyolin-layers are connected
by a number of thickened junctions, which tend to occur
in groups and which are arranged in radial rows. In surface
view these junctions appear as groups of dark spots on the
conchyolin-layers ; in radial section they are as shown in fig. 37,
and can also be seen in Pl. XX XVI. fig. 13. These junctions
seem to be thickenings of the walls which normally connect
the several conchyolin-layers of the nacre to one another; they
may, in fact, be regarded as local exaggerations of the condition
described as “ granular repair-nacre.”
It is interesting to note the peculiar manner in which these
repair- _substances occur in Japanese “Culture Pearls.” ‘This
name was given by the late Professor Mitsukuri (27 ¢, pp. 283-4,
pl. xi. fig. 1) to pearl-like bodies—‘ blisters,” as they would be
called on the Australian fisheries—which are artificially produced
in the Japanese Pearl-Oyster, Margaritifera martensii * Dunker.
The production of these “‘ Culture Pearls” is an extensive
industry supporting about 100 persons, and is carried on by
Mr. Mikimoto on leased areas of sea-bottom in the Bay of Agu,
Shima Province, on lines originally suggested by Prof. Mitsukuri
in 1890. It has been going as a commercial success since 1898,
when the first crop of ‘ Culture Pearls” was marketed. In 1905
the number of oysters operated on per year was from 250,000 to
300,000.
The process, which is protected by patents, is analogous to that
adopted by the Chinese in the production of “ Buddha Pearls”
in the fresh-water mussel, Dipsas plicatus, and to the method
discovered by Linnzeus in the 18th century (see Herdman, 16 a),
and consists in the introduction between the shell and the mantle 7
of a bead of nacre, which in due course (the time allowed in
Japan is four years) becomes thickly coated over with nacre,
* This molluse is regarded by some naturalists as a local race of M, vulgaris, to
which it is undoubtedly very closely related. Whether it be called WM. martensii or
M. vulgaris var. martensii is largely a matter of individual taste.
+ This is apparently done vid the edge of the shell and not by drilling as in the
Linnzeus process.
[59j
318 DR. H. LYSTER JAMESON ON
forming a hemispherical, or sometimes rather more than
hemispherical pearl-like excrescence, attached to the shell by its
base. These ‘Culture Pearls” are produced in large numbers,
and find a ready market for purposes for which “ half-pearls” are
used. ‘They are now familiar objects in Europe *.
Text-figure 39 is a section of a Japanese ‘“ Culture Pearl,”
which I purchased in London, while still attached to the shell,
and decalcified.
Text-fig. 39.
pr col.
col! ae G7:
Section through a decalcified Japanese “Culture Pearl” still attached to the shell.
nu., the artificial “‘ nucleus,” a bead of nacre, the amine of the nacre being
cut transversely ; pr., prismatic layer; xac., original nacreous lining, which
existed before the nucleus was introduced ; nac.', more recent nacre, lining the
shell and extending over the “nucleus” to form the “Culture Pearl,”
secreted after the introduction of the nucleus; nae.’’, nacreous layers where
the lining of the shell is carried over the nucleus; col., col.’, repair-substance
secreted in a zone around the point of contact between nucleus and shell,
where the deposition of the shell-substance was not controlled by the
mantle; gr., granular matter, perhaps of foreign origin or of the nature of
amorphous substance. XX 10.
The “ nucleus” has been very skilfully introduced, so that there
is practically no trace of “dirt” between it and the nacreous
layer with which it is invested, as is so often the case in the
“ blisters ” which have been produced by naturalists and experi-
menters from time to time. Moreover, the disturbance of the
normal functions of the mantle has been so slight that, in the
* Needless to say, these bodies are not “ Pearls,” biologically speaking, but
belong to the class of structures to which I have applied the naine “ blisters,”
familiar on the Australian Fisheries and in the Trade. Various naturalists have
produced such bodies from time to time. Ihave recently seen some very beautiful
ones produced in Margaritifera maxima, and I myself produced some presentable
ones in Margaritifera margaritifera in Papua in 1899-1900. But although
attempts have been made, and are still being made, to do this on a commercial scale,
T am not aware that commercial success has yet been achieved anywhere else than
in Japan; indeed, I think that the combination of circumstances which has led to
the success of the Japanese enterprise—viz., skill, patience, and intelligence, backed by
the best scientific advice and supported by cheap labour—has generally been lacking
in other ventures. J may add that the price that could be obtained for the best of
these gems is insignificant compared with the value of a real pearl of like size. No
[60]
THE CEYLON PEARL-OYSTER. 319
particular sections that I examined, there was a marked absence
even of the repair-substances. But in the zone immediately
around the point of contact between nucleus and shell, where,
when the nucleus was introduced, the epithelium of the mantle
was presumably unable to fit closely against the surfaces, it is
otherwise. Here, on examining the whole “ Pearl” as a trans-
parent object after decalcification, an opaque ring or zone was
distinctly visible. This was due to the presence of granular
matter, perhaps derived from the exterior, perhaps from the
tissues of the animal (text-figs. 39 & 40 B, gr.), and to very
irregular columnar and amorphous repair-substance (col., col.’).
his columnar substance is shown in greater detail in text-fig. 40,
A & B, corresponding respectively to col. and col.’ in text-fig. 39.
In text-fig. 40, A, in the niche between the nucleus and the shell,
where the mantle-epithelium could not reach, we see the product
of its secretion consolidated away from the influence of the
epithelium. Here the columns, instead of forming the character-
istic palisade-lhke structure, with their long axes perpendicular
to the secreting surface, are arranged in groups suggesting
incomplete spheerocrystals.
The curious fan-like arrangement which the columns take on in
text-fig. 40, B, suggests that the repair-substance arose through an
extravasation of the shell-forming fluids at the point a, the layer
nac.' representing the first normal nacre, secreted by the mantle
when it occupied that position, the irregular columnar and
amorphous substance being due to the consolidation of the
secretion which filled the space, triangular in section, which lay
between the nucleus (nw.), the shell (nac.), and the mantle; the
position occupied by the last named being represented by the layer
of nacre marked nac’.
(13) Varrerres or Ceyton Prarts.
Pending a classification based on the nature of the causes
which give rise to the formation of the pearl-sac, I propose,
following Herdman, to separate the pearls which I have examined
in or from the Ceylon Pearl-Oyster into two main groups,
accordingly as they typically occur clustered in the neighbourhoods
really satisfactory proof has ever been given that free spherical “pearls” can be
produced in this way, though Prof. Mitsukuri (/.c.) says that there are some hopes
that this will be done. There is no theoretical reason why a modification of the
Japanese or Linnean operation should not be devised which would achieve this end—
indeed, there is some reason to think that Linneus actually did produce some round
“pearls” and not only “blisters.” But such bodies, if produced, would not be
“pearls” in the strict biological sense, though it is quite likely that they would be
marketed as such in quantities before the difference was detected.
Since writing the above, I have been informed by Mr. 'Toyozo Kobayashi, Professor
at the Tokyo Higher Technological College, who is associated with Mr. Mikimoto
in his enterprise, that perfectly free “ pearls” have been produced by these methods
within the last two years, but so far only exceptionally, and on a scale so small as
not to be applicable commercially.
[61]
320 DR. H. LYSTER JAMESON ON
of the muscular insertions or singly in the non-muscular parts of
the body-wall and mantle.
Text-fig. 40.
“ = if DE :
Bs
A. The irregular columnar and amorphous substances, shown at col. in text-figure 39.
nac., nacreous lining of the shell; nae.’, nacre deposited shortly after intro-
duction of nucleus, passing over into the repair-substance (¢r.) ; nae.’’, nacre
continuous with the layers investing the nucleus; col., col.’, columnar repair-
substance; am., amorphous repair-substance. X 35.
BR. The fan-shaped mass of repair-substance, shown at col.’ in text-figure 39.
nu., the introduced “nucleus”’; nac., the original nacreous lining of the
shell; nac.’, the first layers of nacre, separated after the introduction of the
nucleus; cpl., columnar repair-substance; am., amorphous repair-substance ;
gr., granular matter, perhaps of extraneous origin. > 100.
[62]
THE CEYLON PEARL-OYSTER. Bp
T adopt Professor Herdman’s term ‘ Muscle-Pearls” for the
former class, while for the latter category I propose the name
‘“* Parenchyma-Pearls ”*, because they occur typically in the
parenchymatous subepidermal tissues of the non-muscular parts
otf the body-wall and mantle, or, by secondary displacement, in
the more deeply seated soft tissues.
This group corresponds, I think, to Herdman’s “ Cyst-Pearls,”
but I prefer not to adopt the latter name, as, if the word “ cyst”
refers to the encysted Cestode, which Herdman associated with
pearl-production, I have been unable to trace the connection
between it and the pearl; while if it refers to the pearl-sac or
“cyst,” this is found around all pearls, including muscle-pearls.
There is some reason for believing that some par renchyma- -pearls
arise from causes different from those that lead to the formation
of muscle-pearls, and, indeed, it is quite possible that parenchyma-
pearis have several modes of origin, as Herdman believes ; but,
on the other hand, their differences may be due in great measure
to the different parts of the tissues in which they originate,
and it is certainly quite impossible, in many cases, to say, from
the structure of a pearl and of its nucleus and pseudo- nucleus,
whether it is a “ muscle-pearl” or a “ parenchyma- -pearl.” W ith
regard to Herdman’s “ Ampullar pearls,” I cannot regard this
group as of equal value to the above two classes, as, in my
experience, so far as it goes, the ““Ampulla” is of secondary origin,
due to the absor ption of the tissues intervening between the pearl
and the shell, and to the epithelium of the pearl-sac and that of
the outer face of the mantle thus becoming continuous.
Before going further I had better explain a term that I am
introducing into this paper. I am_ restricting the word
‘* Nucleus,” as applied to the body found in the centre of a
pearl, to those bodies which appear to be either of foreign
origin or derived from the pearl-oyster otherwise than through
the agency of the shell-secreting mechanism. To the bodies
formed by the shell- and _pearl- -secreting mechanism, composed,
asa rule, of different kinds of repair- -substance (bodies which
have no doubt often been wrongly mistaken for objects of foreign
origin), I propose to apply the name “ Pseudo-nucleus.” I have
endeavoured to be consistent in the use of these two terms, but,
as is so often the case in biological matters, there is at times a
difficulty in defining a sharp boundary-line between the objects
to which they are respectively applied.
A. Muscle-Pearls.
I have set out above (p. 267) Professor Herdman’s views on
the nature and origin of these. Briefly recapitulated, they are
the following. From some unknown cause, minute calcareous
* Rubbel (34 a) applies the term “ Mantelperlen” to these bodies, a term which
I prefer to mine, though it is too late to alter the nomenclature in this paper.
Proc. Zoou. Soc.—1912, No. X XI. 2)
[63]
322 DR. H. LYSTER JAMESON ON
depositions or ealcospherules * arise in the tissues, close to the
attachments of the muscles to the shell. Ectoderm-cells may
“ migrate to the source of irritation, and thus be responsible for
the deposition of a pearl.” No explanation of the origin of these
calcospherules is given, but Mr. Southwell thinks it is ‘almost
certain that they are depositions from the blood,” and refers to
them elsewhere as “ of excretory origin ” (42).
I have been led by my observations to take a quite different
view of these ‘ calcospherules” +, and as their origin is so closely
related to that of Muscle-Pearls, | cannot do better than begin
the present section of my paper with an account of their struc-
ture and origin.
According to my view, Prof. Herdman’s ‘ calcospherules ” are
not free concretions at all, but are minute pearls, composed of
hypostracum ; and I propose, therefore, to call them “ hypostra-
cum muscle-pearls,” to separate them from “ nacreous muscle-
pearls.” As stated by Herdman, these bodies occur close under
the epidermis (unless secondarily displaced, e. g. by the addition
of new ones), and I usually find them in the region where the
muscle-attachment epithelium passes over into the ordinary shell-
secreting epidermis of the mantle. A group of these hypo-
stracum-pearls is shown on Pl, XX XIX. fig. 22, which represents
a portion of the mantle-musculature of one of the unlabelled
specimens in the British Museum, examined entire in oil of
cloves. The same pearls, decalcified, are seen in fig. 23. These
little bodies measured from 0:02 to 0°5 mm. in diameter. In
Pl. XX XVIII. fig. 19 similar bodies, hy.p., are seen in a section
along with ordinary nacreous muscle-pearls; while single indi-
viduals are shown in Pl. XX XIX. figs. 21 & 21a@and Pl. XL.
fig. 25. Sections ground from these bodies, or cut from the organic
residues left when they are decalcified, show them to be composed
of the same substance as the hypostracum of the shell. They
consist of calcium carbonate, in fine fibrocrystalline form, showing
radial and also concentric markings, with a small central cavity
(Pl. XX XIX. fig. 21a). Decalcified they also resemble hypo-
stracum in all details of structure and reaction to stains
(fig. 21). Their organic basis stains more blue with hematoxylin
than the organic parts of the other shell-substances, and takes up
carmine more deeply. Their alveolar structure is also much finer
than that usually found in the columnar varieties of repair-
substance, so fine, in fact, that in surface-sections the reticular
structure seems almost like that of the protoplasm itself. As has
been observed in the hypostracum of the shell, this substance
sometimes passes over into nacreous conchyolin laterally. The
* This word is presumably intended to convey the same idea as the word
“concretion” adopted by me (25) in 1902, i. e. a spherocrystal-like body arising in
the tissues otherwise than by epidermal secretion; and therefore analogous to
cholesterin calculi, etc. (ef. Harting’s “ Calcospherites,” 12).
+] find that Rubbel (34 a), working on the freshwater Pearl-Mussel,
Margaritana, has arrived independently at the same view of the nature of these
bodies as that here propounded.
[64]
THE CEYLON PEARL-OYSTER. 323
central cavity of a hypostracum-pearl may contain granules of
doubtful origin, as in the case shown in fig, 21, but it is frequently
quite empty. At times the organic basis of one of these hypo-
stracum-pearls, when decalcified, shows a tendency to break up
into segments, especially at its inner surface; the segments in
such cases probably correspond to the outlines of the original
secreting-cells ; indeed, in such cases the whole body may have
an almost cellular appearance, which is not surprising in view of
the generally accepted theory that the hypostracum arises by
direct transformation of the muscle-attachment epidermis.
These hypostracum-pearls shrink, on decalcification, to about
one-third of their original diameters (Pl. XX XIX. figs. 22 & 23).
When the tissue is old and defectively preserved, as in this
reparation and in that shown in fig. 19, they come away from
the wall of the enclosing sac during decalcification ; but in better-
preserved material, where the connection between the muscle-
attachment epithelium and the pearl is maintained, the organic
basis of the decalcified hypostracum-pearl remains attached to the
wall of the sac (Pl. XXXYV. fig. 8). Nacreous pearls, on the
other hand, almost always shrink away from the sac on decalci-
fication.
The smallest of these hypostracum-pearls that I observed
measured about 0°02 mm. in diameter.
As the muscle-attachment epithelium, in Margaritifera at any
rate, takes at most a very small part in shell-thickening, the size
of these hypostracum-pearls is limited by the maximum thickness
to which hypostracum normally attains. For further growth to
occur, resulting in the formation of a nacreous muscle-pearl, it is
necessary for some of the nacre-secreting epidermis to be present
also (Pl. XXXYV. figs. 8, s., & 9; Pl. XXXVI. fig. 10, sac.).
Fig. 8, from a specimen given to me by Prof. Herdman, shows
above a nacreous muscle-pearl and below a hypostracum muscle-
pearl. Here we have a cyst, which is more or less spherical, and
contains a large central cavity lined with a substance which is
indistinguishable from the organic basis of hypostracum. Where
an epithelium can be detected in the wall of the cyst (m.ep.') it
possesses all the characters of muscle-attachment epithelium, its
cells being continuous with the muscle-fibres, m., on the one
hand, and with the hypostracum, fy., on the other. In some
‘ases the muscle-attachment epithelium can be traced on all sides
of the sac; in others, as in fig. 8 and fig. 10, ¢., only at certain
parts. In still others nosuch epidermis isrecognisable, I think,
however, it is safe to assume, whether the hypostracum-pearl is
surrounded by a sac of attachment-epidermis or not, that such a
pearl can only arise where such a sac is present ; and it is easy
to detect the epithelium in most of the better-preserved examples
(figs. 8, 9, & 10, m.ep.). Still, in some of the fairly well-preserved
preparations I can identify no such epithelium. ‘This is the case
in Pl. XXXVI. fig. 11. In this example, which is on one of
Prof. Herdman’s slides the hypostracum- pearl, which measures
? « ’
21%
324 DR. H. LYSTER JAMESON ON
80 p in diameter, and has a wall about 10 » thick, lies close to a
nacreous muscle-pearl, about 1 mm. in diameter, ‘ne sae of which
is shown at ep.p.s. The cyst is embedded in a strand of muscle
traversing the mantle-parenchyma obliquely, and ending in muscle-
attachment epidermis which was attached to the shell. (Such
connections between the general musculature of the mantle and
the shell occur here and Pere quite apart from the more regular
muscle-scars. For examples of this in J/ytilus see List, 27 b,
Pl. 8. fig. 1.) The cyst contains at one point a little ereralet
mass. ‘The muscle-fibres here appear to be in direct contact with
the hypostracum. The easiest explanation of this condition would
seem to be the hypothesis that the original epithelium has dis-
appeared. It is not difficult to suppose that a highly specialised
“tendinous ” epithelium, like the attachment-epidermis, whose
fate seems to be to become a part of the shell, is incapable of
regenerating itself, and, therefore, destined to die and disappear
on ceasing to be functional. If we take this view, the typical
hypostracum- -pearl is not so much a stage in the dev elopment of a
nacreous pearl as a phase parallel with it; the latter arising when
the original sac contains some of the ordinary n nacre- secreting
epidermis, or cells capable of giving rise thereto, the former when
it is composed of attachment- epithelium alone. The hypostracum-
pearl would thus have a limited growth, the nacreous pearl an
unlimited growth. However, in considering these cases where
there does not appear to be any attachment-epithelium, it must
be remembered that this particular epithelium is often very difficult
to see, so that some workers have even failed to detect its existence
on the regular muscle-insertions. Much light can no doubt be
thrown on these questions by a really thorough study of the
behaviour of the cells at the places where the muscle-attachment
epithelium goes over into the ordinary epidermis of the mantle,
and of the histological phenomena associated with the wandering
of the muscle-attachment. The material of the pearl-oyster that
T have examined so far is not sufficiently well preserved to allow
of such study. So far as I know, this important matter has never
been properly investigated in any molluse.
T will now pass from the hypostracum muscle-pearls to the
nacreous muscle-pearls. ‘Typical instances of these are shown in
Pl. XXXV. figs. 8&9 and Pl. XXXVI. fig. 10. These three
examples are all explicable as derivatives of the hypostracum-
pearl. Figs. 8 & 10 obviously lie in the borderland between
one of the ‘regular muscles and the parenchyma (fig. 8 is at the
insertion of one of the pedal levators). Fig. 9, from one of
Prof. Herdman’s slides, is in a place in the free mantle where a
few small muscle-strands (musc.) are attached to the shell. The
sac of each of these pearls is lined in part by ordinary nacre-
secreting epithelium, underlying which is the typical granular
parenchyma, in part by muscle-attachment epithelium, continuous
with the musculature. As the former is much more active than
the latter, these pearls are all eccentric in shape, having a hilum
[66]
THE CEYLON PEARL-OYSTER. 325
of hypostracum at one side, which, unlike the nacre, does not
increase appreciably in thickness. The centre of each is a cavity,
which in figs. 8 & 10 is obviously lined with hypostracum, and this
hypostracum is connected by a plug of the same substance with the
remaining muscle-attachment epithelium. In fig. 9 the growth
of the nacre has pulled down the plug of muscle-attachment
epithelium into the hilum, and produced quite a long strand of
hypostracum-like substance. The presence of these hila, together
with the effect of the mutual pressure of muscle-pearls when
crowded together, has much to do with the generally irregular
shape of commercial seed-pearls. Fig. 10, also from one of
Prof. Herdman’s slides, shows a very early stage in such a muscle-
pearl, with a small cyst-lke hypestracum- pearl alongside it. Here
the ordinary epithelium of the sac seems to be gaining on the
muscle-attachment epithelium.
These muscle-pearls always contain a central cavity, which may
be broken up by trabecule of hypostracum-like substance or of
conchyolin, this substance being continuous with that forming
the lining of the cavity. The cavity, like that of the pure
‘hypostracum-pearl, may be empty or may contain more or less
granular matter.
Muscle-pearls are often clustered and may be very numerous.
Thus the old unlabelled material in the British Museum has
dense clusters of these pearls in some places, and so has some of
Dr. Kelaart’s material.
It is by no means the case that muscle-attachment epithelium
always persists in the sac of a muscle-pearl. The whole sac
may pass over at an early stage into nacre-secreting epithelium,
a process which is, perhaps, analogous to what occurs in the wake
of an advancing muscle in the growing shell. This was apparently
the case with the pearl that occupied the sac adjoining the body
shown on Pl. XXXVI. fig. 11. The nucleus of this pearl is
shown at fig. 12 on the same plate. The central portion of this
pearl is composed of irregular conchyolin-like substance, which
cannot be identified as hypostracum, and which quickly
gives place to ordinary nacreous substance (7.). In the neigh-
bourhood of this pearl is another, not figured here, the centre of
which was comparable to the pearl shown on Pl. XX XV. fig. 8;
this pearl had become more spherical secondarily by the dis-
appearance, in the course of its growth, of the muscle-attachment
epithelium. It is hard to conceive that these two pearls, and the
hypostracum-pearl associated with them, are not all of similar
origin.
Pl. XXXVI. fig. 13 shows the centre of another pearl, perhaps
a muscle-pearl, from the mantle-margin, in one of Prof. Herdman’s
slides. This pearl appears to have measured about 2 mm. in
diameter. The central cavity is about 0:1 mm. in its greatest
diameter and is lined by abnormally thick conchyolin-like
substance. Outside this are layers of ordinary nacre, which pass
over into a form of repair-nacre showing radial markings,
[67]
326 DR. H. LYSTER JAMESON ON
probably due to variations in the rate of secretion of the con-
stituent substances. This zone is 0°03 mm. thick. The central
cavity is empty, except for a few granules.
In this case the muscle-pearl, if such it is, does not contain a
pseudo-nucleus composed of hypostracum or a spherocrystal-like
body such as those shown in figs. 19 & 20; and the real
“nucleus” of such a pearl might be said to be a cavity which may
or may not contain a few indistinct granules, perhaps of foreign
origin,
The same condition is also typical of those pearls which I have
examined from Dr. Kelaart’s material. I have decalcified 38 of
these’ ‘in Valli (Plo XXX Vile fies! 1455, 7 163 Bex XOX VennIe
figs. 17 & 18; Pl. XLIV. figs. 46, 46 a, 47, 47 a, & 48). That these
pearls are of the same nature as the other muscle- -pearls seems
probable from the fact that a few hy postracum- -pearls occur mixed
with the other pearls in Dr. Kelaart’s specimens, and from the com-
plete series of intergradations between the various forms described
above, which is shown by the unlabelled specimens in the British
Museum, described below. Pl. XXX VII. fig. 14 is a section of
Dr. Kelaart’s specimen showing “pearls in ovary.” Hach of
these pearls hes in a cavity which doubtiess was originally lined
with an epidermal epithelium, though this can no longer be
recognised owing to the state of preservation. The cavity is
surrounded in every case bya layer of the granular subepidermal
parenchyma (par.). Some of the pearls have been forced out of
the subepidermal layer, and now lie embedded in the deeper
connective-tissue, in which are seen muscle-bundles and tubules
of the ovary.
Tn each ease the centre of the pearl is a small cavity, containing
a few granules or strands of what appears to be conchyolin ; but
the pearl in the lower right-hand corner contains also some
columnar substance. The irregular conchyolin-like matter is well
seen in the centre of the pearl i in the oe left-hand corner of the
sketch, which is shown enlarged in fig. 15. It is interesting to
note that the series of sections from which these drawings were
made contained an example of the smaller Cestode larva, 7'ylo-
cephalum minus.
Plate XLIV. figs. 46, 46a, & 47, 47a show two pearls
picked from one of Dr. Kelaart’s specimens, decalcified, and
examined whole in oil of cloves (46 & 47) and after being sec-
tioned (46a & 47a), Fig. 46 shows a dense central mass, of
closely laminated nacreous substance, which on superficial
examination might be taken for the remains of a dead parasite,
but a section shows that the whole pearl is composed of nacreous
substance around a small central cavity.
Fig. 47, examined whole, was extremely suggestive of a dead
parasite ; indeed, the concentric lamination of the pseudo-nucleus
was not disclosed till sections were cut. These (fig. 47a),
however, furnished the explanation. The real centre of the
pearl was, as in the rest of Dr. Kelaart’s material, a nacreous
[68]
THE CEYLON PEARL-OYSTER. 32
‘pearly mass, with a central cavity, showing at one side a plug of
conchyolin-like substance. External to the normal central nacre
were some irregular layers, such as one gets on the inner surface
of the shell when a dark blotch or blister is caused by derange-
ment of the secreting epithelium (compare the “ Olflecken” in
Margaritana, Rubbel, 34a). ‘The opaque character of these
layers, some of which were brown through the immigration or
infiltration of what appeared to be cellular matter, others
distinctly columnar (repair-substance), rendered the real nature
of the pseudo-nucleus obscure till sections were cut, Outside
these abnormal and pathological layers typical nacre was sub-
sequently produced, thus giving a normal pearl with a dark
centre.
The same characters are shown on Pl. XLIV. fig. 48, where
the centre of the pearl appears opaque and granular for a similar
reason. In this case the pseudo-nucleus measured about 5 min.
in diameter, and, examined entire, might have been taken for a
dead parasite. It was such a nucleus, coupled with the presence
of Trematodes, probably Muttua margaritifere Shipley & Hornell,
in the tissues of Dr. Kelaart’s pearl-oysters, that, in 1901, led me
to the probably mistaken’ conclusion that a Trematode might be
one of the organisms which afford the stimulus for the formation
of the pearl-sac in Margaritifera vulgaris, as the Trematode
Gymnophallus does in Mytilus * (25, p. 162).
But examination of sections (Pl. XXXVII. fig. 16 and
Pl. XX XVIII. fig. 17) showed that the opaque pseudo-nucleus
was due to a break in the continuity of the nacre; a layer of
granular substance (g7.), apparently dead cells (perhaps of the
nature of the “oil-spots” in Margaritana, or derived from an
immigration of leucocytes such as Moynier de Villepoix observed
(28, p. 112) or from Protozoan parasites), being followed by the
secretion of two horny layers of amorphous repair-substance
(am., am.'), after which normal nacre resumed its development.
The real centre of this pearl, as in the rest of Kelaart’s material,
consists (Pl. XX XVIII. fig. 18) of shreds of conchyolin-like
material, and a few obscure granules, in a cavity which is sur-
rounded first by granular repair-nacre and then by ordinary
nacre.
In the two unlabelled specimens in the British Museum, from
which Pls. XX XVIII.-XL. figs. 19-28 and Pl. XLIV. fig. 49
are drawn, while the pearls agree with those described above in
their clustered habit, occurrence in the muscular regions, and
association with hypostracum-pearls, we have more frequently as
nuclei either hypostracum or special sphzrocrystal-like bodies,
which I regard as formed of columnar repair-substance.
* Fuller knowledge and closer study lead me to doubt the accuracy of my own
observations as to the occurrence of the remains of Trematodes in the pearls produced
by the other species of molluscs referred to on p. 162 of my 1902 paper with the
exception, of course, of Mytilus edulis, in wnich the relation between Trematodes
and pearls is beyond question,
(09)
328 DR, H. LYSTER JAMESON ON
Pl XXXVITITI. fig. 19 shows a group of such pearls, scattered
among which are hypostracum-pearls (hy.p.). The nucleus of
the eccentric pearl at nz.’ is clearly composed, like that of the
incipient pearl shown on Pl. XXXIX. fig. 22, nac., of hypo-
stracum, and resembles the hypostracum-pearl shown at fig. 21,
which has a small quantity of granular contents. One of the
columnar nuclei is shown enlarged at fig. 20. This is the nucleus
of the large pearl shown in the upper part of fig. 19
(Pl. XXXVIII,). Centrally there is a small ae in which a
gr anular mass of doubtful origin is noticeable (g7.). This cavity
is surrounded by an irregular zone of substance which seems to
be the same as the amorphous repair-substance of the shell
(cf. Pl. XL. fig. 29). Externally to this there is columnar
substance, forming a sort of spheerocrystal-like mass, the fibro-
crystalline calcium carbonate being deposited in a conchyolin-like
basis, which, on decalcification of the pearl, remains as a
framework. This substance is seen cut tangentially at one end
of the pseudo-nucleus. Outside this is the normal nacre of the
pearl. In one or two cases the amount of granular matter in the
centre of the pearl was considerable ; thus Pl. XL. fig. 24, which
is taken from the same series as the preceding figures, shows the
central portion of a pearl which has a dumbbellwshaped double
nucleus, the larger half being about +17 mm. in diameter, and
each half containing an opaque brownish mass of dead animal
matter, perhaps of cellular origin, but quite unrecognisable. The
contents of the two cavities were continuous at one point. There
is nothing to suggest that either of these bodies represented a
dead Cestode; I could find no denser portion, such as would
eee occur at the point representing the myzorhynchus, nor
vas there anything that could be safely identified as the cuticle
of the parasite. If the contents suggested anything, it was rather
the remains of a large Protozoan “parasite, containing spore-like
bodies in a plasma. (il xe the Sporozoan spores which Dubois claims
to have identified in the nucleus of a pearl from J/. vulgaris from
the Mediterranean, 7, p. 311, and 8, p. 104); or, perhaps, a mass
of mucus containing a few cells. Each of ee centres was
surrounded immediately by the amorphous substance, this being
followed by, and continuous with, a radially calcified layer, the
bases of the calcareous prisms being evidently embedded in the
amorphous substance, which extended up between them to form
the organic framework of the columnar substance. This condition
is comparable to that seen at t. on Pl. X LI. fig. 30, which shows
the amorphous substance secreted at the junction of two pearls
in a compound pearl, passing over into columnar repair-
substance.
Externally to the columnar layer of the pseudo-nucleus the
normal nacreous layers of the pearl are formed,
The other extreme is shown on PI. XL. fig. 25,a hypostracum-
pearl ‘08 mm, in diameter, the central cavity of whick has no
contents whatever.
[70]
THE CEYLON PEARL-OYSTER. 329
Pl. XL, fig. 26 shows a pearl having for its nucleus a double
hypostracum-pearl, the two constituents being apparently
separated by a mass of amorphous substance. Other examples
were examined which showed intergradations between double
and single hypostracum-pearls,
In fig. 27, from the same preparation as the above, there is a
central cavity, containing a few granules, and surrounded by
amorphous and columnar substances followed by nacre and finally
by hypostracum. In another case in the same preparation the
same state of affairs was shown, but there were further layers of
nacre outside the hypostracum, resulting in a fair-sized pearl.
These cases are of interest as indicating that the attachment of
muscle-fibres to a pearl may arise secondarily, in the course of
its growth. In some cases the columnar substance is stratified,
as in the pearl at the bottom left-hand corner of fig. 19,
Pl. XXXVIIT. andin fig. 49, Pl. XLIV. In Pl. XL. fig. 28, which
is the left-hand pseudo-nucleus of the double pearl shown in
fig. 49, there is at one pole a distinct transition from the columnar
matter of the pseudo-nucleus to normal nacre (nac.’), just as
occurs in the substance of the pearls figured at Pl. X LI. fig. 34
and Pl, XLIII. fig. 43. This pseudo-nucleus is followed by
normal nacre (naec.), after which there is a layer of brittle horny
matter (am.), which I regard as analogous to amorphous repair-
substance ; this is followed by another columnar layer (col."'),
imperfect on one side, and this again by nacre.
A preparation from the second unlabelled specimen in the
British Museum showed, side by side, all kinds of intergradations
between the various kinds of nuclei and pseudo-nuclei of muscle-
pearls described above.
[regret that | am as yet unable to trace the origin of the
muscle-pearls beyond the cyst-like sac, lined with hypostracum
or another form of. shell-substance. One or two preparations
show cavities lined with a few cells, which may represent the
first stages of pearl-sacs. Moreover, here and there, the relations
of the epidermis, at the place where the muscle-attachment
epithelium gives place to ordinary mantle-epithelium, suggest
that these cysts arise by direct invagination at thisregion. What
may be the mechanism which gives rise to this invagination I
cannot say, there are certain indications that suggest that it may
be associated with the presence of parasitic Protozoa, an idea
suggested by me in 1902 (25, p. 162); but until I have been able
to examine better-preserved material, it would be unwise to
hazard yet another theory of pearl-production. At any rate, it
is clear that, if pearls in J/. vulgaris ave of parasitic origin (and
T adhere to the view that the distribution of pearl-producing
examples of this and most other molluscs can at present best be
explained on the parasitic hypothesis), the immediate cause of the
pearl is not the mechanical irritation caused by the body of the
parasite, but rather the toxie properties of its secretions, which
lead to the pathological changes (formation of the tumours that
[71]
330 DR. H. LYSTER JAMESON ON
we call pearl-sacs) in the tissues; and that consequently the
‘cause ” of the pearl is not to be looked for in the nucleus, which
in the Ceylon pearl-oyster frequently does not exist, but rather in
the tissues of the oyster. This is, after all, just what I said
at the bottom of p. 142 in my 1902 paper.
The characters of muscle-pearls may be summed up as
follows :—
(1) They usually and probably invariably arise in close associa-
tion with the epidermis at the point where muscle-attachment
epithelium passes over into normal nacre-secreting epithelium.
(2) They frequently occur several together or clustered in
numbers.
(8) They are typically formed around central cavities in which
granules may be, but are not necessarily, present, and which may
be lined in the first instance with hypostracum, ordinary nacre,
or repair-substances analogous to those which occur where the
normal shell-secreting processes are disturbed.
(4) They are often associated with great numbers of little
bodies, which Herdman calls “ caleospherules,” and which I regard
as minute pearls composed of hypostracum.
(5) They are, according to Herdman, characteristic of certain
of the Ceylon beds; and are, therefore, local in their occurrence,
which would give support to a parasitic theory of their origin.
B. Parenchyma-Pearls (“ Cyst-Pearls,” Herdman).
This class contains a much more heterogeneous group of nuclei
and pseudo-nuclei than the last. The pearls which it comprises
may have arisen from more than one cause, and it 1s more than
likely that a great mz any of the pearls which I refer to it ar e, in
fact, of the same origin as muscle-pearls, but have been produced
singly at spots w here two or three musele-fibres are attached to
the shell, instead of in clusters at the regular muscle-insertions,
and have consequently assumed a spherical form *.
Parenchyma-pearls often show a distinct central nucleus con-
sisting of granules or masses of dark substance which might be
either of parasitic origin or derived from dead tissue-cells (e.g.
leucocytes). In some cases the nuclei of these pearls contain
or consist of grains of sand or other foreign particles. The
nucleus is typically succeeded by one or more layers of repair-
substance, which often intergrades with the normal shell-
substances (nacre ete.) of the pearl. In consequence of the
presence of this abnormal shell-substance the centre of a paren-
chyma-pearl frequently contains a dark, spherical, concentrically
laminated, radially striated pseudo-nucleus, ‘This opaque pseudo-
nucleus has no doubt on many occasions been mistaken for the
remains of a parasite, in pearls decalcified and examined entire ;
but sections generally reveal its real nature unmistakably.
* These occasional attachments of small muscles to the shell on the general
mantle-surface are well known. See e.g. List (27 6), pl. 8. fig. 1.
[72]
i THE CEYLON PEARL-OYSTER. 331
Cestodes may possibly occur in the centres of these pearls at
times, as Professor Herdman maintains, just as grains of sand
and other organic and inorganic particles certainly do; but this
remains to be proved, and my material has afforded no evidence
in favour of this much-quoted theory. And, even if it should
be proved that Cestodes do occasionally occur as the “ nuclei” of
‘eylon pearls, the real causes which underle the development
of the pearl-sae (which is the essential factor in pearl-production)
have still to be discovered. The characters of the centres of
parenchyma-pearls can best be understood by reference to the
next section of the paper, which is largely descriptive of them,
though many of the pearls referred to therein are unquestionably
‘*muscle-pearls,”
(14) Descriptions or THE CENTRES OF INDIVIDUAL PEARLS.
In the absence of evidence connecting them with muscle-
pearls I propose to treat the four pearls from the Persian Gulf,
and the twenty-one pearls purchased for me in Ceylon by the
Ceylon Company of Pearl Fishers, Ltd., as parenchyma-pearls,
and to describe along with them eight of the pearls in Prof.
Herdman’s collection of slides which are not obviously muscle-
pearls. These descriptions will be followed by an account of a
number of samples and collections of pearls from J/. vulgaris
from Ceylon and other localities.
A. Material from the Persian Gulf.
It may be useful to begin with the material from the Persian
tulf. This, so far as it has been examined—for some of my
specimens still remain unopened,—comprised three pearl-bearing
examples, containing four small pearls. All these pearls
appeared to be of the kind classified by Prof. Herdman as “ cyst-
pearls” and by the present writer as ‘* parenchyma-pearls,” as
they seem to have arisen quite independently of, and away from,
the muscle-insertions.
I append a short description of the conditions in each of these
cases.
Preparation LXIV A contained a solitary pearl, about 2mm.
in diameter and slightly lenticular in shape, situate in the left
mantle-lobe, on a level with the anterior end of the attachment
of the outer gill-lamella. Unfortunately, owing to imperfect
penetration in the embedding process, this pearl did not present
a complete series in section. It lay wholly in the subepidermal
parenchyma, which was sharply cut off from the underlying
visceral connective-tissue by a layer of musculature, under which
were the tubules of the ovary. The pseudo-nucleus was a radially
calcified concentrically laminated body, about 3 mm. in diameter,
with a few darkly staining granules in the centre.
The second specimen, Preparation LXIV 3, contained another
[73]
oon DR. H. LYSTER JAMESON ON
solitary pearl, which before calcification measured somewhat over
a millimetre in diameter, but when decalcified shrunk to *7 mm.
It was situated in the left side, in the wall of the visceral mass,
over the stomach. In section (Pl. XLI. fig. 33) the pearl is seen
to le in the subepidermal parenchyma (par. ), projecting a littie
through the muscular coat (msc.) into the visceral connective-
tissue “(c .t.), 12 which the tubules of the ovary (ov.) and muscular
strands to the wall of the stomach (musc.') are seen. The pearl.
sac has been ruptured, presumably by the evolution of bubbles of
carbon dioxide during decalcification.
The pseudo-nucleus, which measures about *3 mm, in diameter,
consists of several layers of columnar substance (col.) formed
around a small central cavity. Probably such a pearl would, as
it increased in size, grow through the muscular layer and
work its way into the visceral mass; indeed, as soon as more
than half its bulk lay on the inner side of the superficial
musculature, the action of these muscles would tend to force it
into a deeper position, where, relieved from the pressure of the
shell, it would stand a better chance of growing into a perfectly
spheri ical ‘‘ fine pearl.”
Preparation LXIV c, the third of these pearl-bearing examples
from the Persian Gulf, contained two pearls, of minute size, about
2mm. apart on the left side. Each was rather less than 1 mm.
in diameter ; one was round, the other elongated. Both lay in
the subepidermal parenchyma, separated from the ovary by the
usual muscular sheath of the visceral mass. Both had pseudo-
nuclei of columnar substance. That of the more elongated one
is shown in Pl. XLI. fig. 34. It has a central cavity, with
irregular granular contents (gr.), surrounded by a number of
layers of nacre (2ac.), outside which is a complete layer of columnar
substance (col.) which is coated on two sides by nacre, passing
over at the two poles corresponding to the longest axis of the
pearl into further coats of columnar substance (col.'). The
transition from nacre to columnar substance is very, well
seen.
The centre of the second pearl in this example was also
composed of columnar substance, formed around a central granular
mass. ‘The granular mass measured about ‘02 mm. in diameter,
the whole centre or pseudo-nucleus °3 mm. These preparations,
apart from the difficulty of obtaining material from the Persian
Gulf, are of interest as showing that the nuclei or pseudo-nuclei
of the pearls produced by M. vulgaris in these waters do not
differ from those of the pearls produced by the same species in
Ceylon.
B. Pearls purchased in Ceylon.
T will now proceed to a short account of the nuclei and pseudo-
nuclei of the twenty-one pearls purchased in Ceylon. All of
these were decalcified, examined entire in oil of cloves, and
drawn. Eighteen of them were also sectioned. (The drawings
[74]
THE CEYLON PEARL-OYSTER. 333
of those not figured here are retained with the slides for
reference.)
(a) One (Preparation XLV) had no obvious nucleus or pseudo-
nucleus.
(>) One (Preparation XLITT) had a small spherocrystal-like
centre of columnar substance, with no foreign contents
(Pl. XLV. figs. 50 & 50a and Pl. XLI. fig. 35).
(c) Three (Preparations XL, XLIV, & LIV) had what appeared
to be irregular masses of amorphous shell-substance, in
central cavities, passing over into repair-substance (PI.
XLV. figs. 53 & 53a; Pl. XLVI. fig. 57; and Pl. XLII.
fig. 40).
(zd) Three (Preparations XLVITI, LITT, & LIV c) had central
cavities containing more or less granular matter, the
character of which could not be determined, but which
suggested dead organic particles (Pl. XLV. fig. 52 and
Pl. XLII. fig. 36). This was surrounded by repair-
substance of columnar structure.
(e) One (Preparation LIV 5) had in its central cavity granular
matter in which diatoms, fragments of sponge-spicules,
(?) minute sand-particles, and vegetable débris were present.
These were surrounded by columnar repair-substance
(Pl. XLITI. fig. 44).
(f) One (Preparation LIV) had, in the otherwise indis-
tinguishable granular contents of the central cavity, a
fragment of a Radiolarian shell (PI. X LITT. fig. 45).
(7) Four had undoubted sand-grains, forming the nuclei around
which the pearl was laid down (Preparations LIT,
LIV a, LIVu, & LIV1). The largest diameters of
the sand-grains in these four cases measured, respectively,
‘Sy nim., “oo x<- lomm:, “Gmm., and “3 mm. CE ee
figs. 54 & 54a; Pl. XLVI. figs. 55 & 56).
(x) One (Preparation LIV x) had a large spherocrystal-like
pseudo-nucleus of repair-substance, intergrading with
nacre, and a central cavity which had been partly
obliterated in cutting the sections, but apparently con-
tained several small quartz-fragments.
(2) Six pearls (Preparations XLII, LI, LIVs, LIVp,
LIVe, & LIV Fr) had, in their centres, bodies which
were so hard that they broke away in sectioning, and were
unfortunately not returned to me with the sections. The
probable diameters of these bodies in the first five pearls
were respectively -45mm., *2mm., ‘1 mm., -25mm., and
“6mm. Preparation LIV Fr had a pseudo-nucleus of
amorphous substance so dense that it broke away. In the
eases of XLIT, LIV, and LIV a, I feel pretty sure
that the nuclei here too were grains of sand, the others
may have had either sand-grains or abnormally bard
amorphous substance in their centres (Pl. XLV. fig. 51 ;
Pl. XLII. figs. 37-39).
[75]
334 DR. H. LYSTER JAMESON ON
Turning now from the “ nuclei” of these pearls to the “ pseudo-
nuclei” which surround them, these do not appear to present any
characters which cannot be expressed in terms of the several
pathological varieties of shell-substance described above. Thus
Pl. XLII. fig. 44 shows the nucleus (composed of diatoms, etc.)
surrounded by typical amorphous and simply columnar repair-
substanee, followed by ordinary nacre. This appears to be
equally the case in Pl. XLVI. fig. 55, where the nucleus is a
sand-grain.
Pl. XLI. fig. 35 and Pl. XLV. figs. 50 & 50a, which had
no foreign nucleus, Pl. XLII. fig. 36, Pl. XLV. fig. 52 with
granular contents in a central cavity, and Pl. XLII. figs. 37-39,
in which example the nucleus was a sand-grain, and Pl. XLV.
figs. 51 & 53 and Pl. XLVI. fig. 56, show these pseudo-nuclei to
be composed of varieties of the columnar substance, Fig. 57
(Pl. XLVI.) and figs. 40-42 (Pls. XLII. & XLII.) show it
highly stratified, and presenting every gradation from amorphous
to prismatic substance. This preparation is a ‘ brown pearl,”
yather over 3 mm. in diameter, composed of the prismatic shell-
substance, and probably produced in the mantle-margin. It
consists of an outer zone, clearly identical in characters with the
prismatic layer of the shell, and showing three distinct series of
prisms. The bases of the innermost layer of prisms are shown in
fig. 42, pr. Inside this normal prismatic substance is the “ pseudo-
nucleus,” which consists externally of a layer resembling in every
respect, except the diameters of its constituent elements, the
prismatic layers (figs. 41, 42, col.). Internally this passes over,
through a substance resembling irregular columnar repair-substance
(fig. 41, tr.), into amorphous substance containing columns or
scattered depositions of carbonate of lime (figs. 40, 41,am.). In
places these bodies are ranged in radial rows, and the amorphous
substance nearly reaches a stage which could be called columnar
substance.
Just around the centre (fig. 40, col.) typical columnar substance
occurs, passing over internally into amorphous — substance.
Owing to the impenetrability of the amorphous substance, the
calcium carbonate has not been dissolved in the deeper layers of
the pseudo-nucleus, and it is seen in the nucleus itself to occur in
the form of perfect rhombohedra, a form I have never seen it
take on in the alveoli of the normal or abnormal shell-substance.
The resemblance of this pearl to the brown Scotch river-pearls
(e. g. that figured by me in ‘ Nature’ for Jan, 22nd, 1903, p. 281
{26}]) is striking.
Preparation XLII, from which figures 50 & 50a on Pl. XLV.
and fig. 835 on Pl. XLI. are drawn, showed an oval central body,
about *6 mm. long, forming a ‘“ pseudo-nuecleus.” On superficial
examination this nucleus is highly suggestive of a Trematode
(fig. 50). But sections showed it to consist of a small sphero-
erystal-like body (fig. 35) about ‘08 mm. in diameter, surrounded
by granular repair-nacre.
THE CEYLON PEARL-OYSTER. 335
Figure 51 shows a pearl, the “ pseudo-nucleus” of which is
produced out in one direction as a strand of columnar and
granular repair-substance extending through the pearl. This
columnar substance is seen to pass over laterally into the ordinary
nacre, and no doubt corresponds to an area in the pearl-sae at which
the normal secretion-processes were disturbed. ‘This was one of the
examples in which the real nucleus broke away.
Fig. 36 on Pl. XLII, which is the centre of the pearl shown
in fig. 52 (Pl. XLY.), enlarged, shows interesting transitional
substance at one pole. This is further enlarged at fig. 43, Pl.
XLIII. The pseudo-nucleus is seen to be discontinuous with the
later-deposited shell-substance, a condition of things which is
sometimes found, and which seems to suggest a pause before the
epithelium becomes properly functional.
Plate XLV. figs. 53 & 53a show a pearl with a spherocrystal-
like pseudo-nucleus, the longest diameter of which slightly
exceeded 1mm. In this case the columnar substance was very
minutely reticulated and fell into three distinct zones. The
pearl is interesting, as showing at one side a patch of columnar
repair-substance apparently continuous with the nacreous layers,
secreted over some foreign matter (granules) that had found their
way into the pearl-sac during the course of the pearl’s growth ;
this columnar substance formed a small “blister” in the substance
of the pearl.
Where a sand-grain is present as nucleus, it appears to be
followed, as a rule, by repair-substance; but in Pl. XLV. fig. 54
this is hardly discernible, except at one pole. This was a pearl
which was drawn entire, and sent to be sectioned, when it was
found that the nucleus broke away and resisted cutting. This
nucleus was returned to me, and proved to bea siliceous sand-
grain (fig. 54a), measuring about "8mm. in diameter. It was
surrounded by an opaque substance, probably “ amorphous repair-
substance.”
Fig. 56 (Pl. XLVI.) shows a sand-grain which measured
about *385 x °25 mm. surrounded first by amorphous substance,
then by stratified columnar substance.
Fig. 55 (Pl. XLVI.), taken from a pearl which I have
preserved entire, shows a pyriform sand-grain, °66 x °5 mm.,
surrounded by a thin layer of columnar substance, followed by
nacre.
Figs. 37-39 (Pl. XLII.) are from the capsule surrounding
a nucleus which broke away and was probably a sand-grain.
Here, again, we have first the amorphous substance, passing
over into “columnar” substance of spherocrystal-like form, with
regular alveoli, which are approximately equal in length, breadth,
and depth.
Figures illustrating minor varieties of the repair-substance as
it occurs in the shell, in the pearl, and in the pearl pseudo-nucleus
might be multiplied indefinitely, but I think enough have been
given to illustrate my contention that these dark spherical bodies,
[77]
336 DR. H. LYSTER JAMESON ON
which so often suggest parasites, are usually in the Ceylon Pearl-
Oyster pseudo- nudlet of spheerocrystal- -like structure, each of
which is reducible to a certain amount of amor phous non-
calcified matter forming the lining of the nuclear cavity
(figs. 35, 36, 37, 40, 41, & 44, am.), and the same substance, some-
times stratified, Borne unmce not stratified, containing depositions
of calcium carbonate. It may be necessary to differ entiate these
pseudo-nuclei into two groups, typically represented by figs. 36
and 40-42 respectively—the one secreted in all probability before
the epithelium of the sac could control its deposition at all (and
thus comparable to a “ Harting’s Body”); the other secreted by
an already partly functional epithelium, When material with
pearls in various stages of formation in situ in the tissues is
available, this dishmnction may prove to have an important
relation to the actual processes by which the pearl-sac arises, and
to the difference between the nuclei of muscle-pearls and some
parenchyma-pearls.
The most remarkable thing about this lot of pearls purchased in
Ceylon is the high pereentage which have as nuclei grains of
sand or other foreign bodies. These cases might cer tainly be held
to give support to the old theory that the Saennletion of any in-
trusive particle, if it occurs at the right place, may give rise to a
proliferation of epidermis resulting in the formation of a pearl-sac
and a pearl, But, on the other hand evidence is not lacking that
the matter is by no means so simple as this. I am instituting
some experiments on J/ytilus (in connection with investigations
on the life-history of the pearl-inducing Trematode that I am
carrying on with the aid of a Goverment Grant) which will, I
hope, throw some light on this question. It is idle to speculate,
without experiments on living molluscs, whether these particles
enter the tissue (@) in connection with mechanical i injuries to the
shell, as Herdman suggests, or (6) from the intestine, by perfora-
tion or the wall, and escape of such bodies as are seen in figs. 44
& 45 (Pl. XLIIL.) into the blood, or (ce) through lesions of
parasitic origin.
With regard to the last-named figures, it is interesting to note
that so long ago as 1857 Kelaart (277) suggested that the siliceous
skeletons of diatoms might become the nuclei of pearls.
Professor Herdman’s Slides.
Professor Herdman’s preparations, illustrating pearls, which he
very kindly lent me, consisted (omitting a few preparations of
clustered hypostracum-pearls) of 24 slides, showing about 25
pearls in section. Of these pearls 13, representing ( preparations,
were obviously muscle-pearls, some of which are shown in figs. 9—
12 (Pls. XXXV. & XXXVI.). In four of these preparations the
eyst-like hypostracum- pearls were also present.
Kight pearls which were not obviously muscle-pearls, repre-
senting six preparations, are briefly described below.
(a) A pearl described in the label of slide as a “ muscle- -pearl.”
[78]
THE CEYLON PEARL-OYSTER. Sob
Tt was about 1°3mm. in diameter, and situated in the body-
parenchyma over the ovary (as in the Persian Gulf examples
described above). The centre was a mass of concentrically
laminated columnar substance, passing over externally into nacre
and about 0-5 mm. in diameter. I treat it here provisionally as
a parenchyma-pearl, as there 1s nothing to suggest that it is a
muscle-pearl.
(6) This was a nice little spherical pearl, well out in the
mantle. ‘The centre was a spherocrystal-like body, of the same
nature as those shown in figs. 35 & 36 (Pls. XLI.& XLII). There
were no recognisable foreign contents,
(c) This showed a pearl in the parenchyma over the ovary, as
in the Persian Gulf specimens, with, apparently, all the characters
of a ‘ fine pearl.’ It had a large dark pseudo-nucleus, 0-4 mm. in
diameter, much like that shown on Pl. XLVI. fig. 57. There was
a central cavity, 0°025 mm. in diameter, containing a small
granular mass; this was followed by nacre, then stratified
columnar substance, then nacre again.
(d) Showed two pieces of free mantle, sectioned, one with one
and one with two pearls iz situ. In the case of the former the
pseudo-nucleus was incomplete, but could be seen to be composed,
in part at least, of columnar repair-substance. In the other
specimen, both pearls had centres resembling those in Dr. Kelaart’s
material, and may well have been muscle-pearls.
(e) The central part of this pearl is shown on Pl. XXXVI. fig. 13.
The pearl is quite close to the mantle-margin, in the musculature.
In the centre there is a eavity with a few granular contents.
This is surrounded by what appears to be ordinary nacre, then
nacre with radial reinforcements, then nacre again. It suggests
a muscle-pearl rather than a parenchyma-pearl.
(f) Contained a pearl, near the mantle-margin, the pseudo-
nucleus of which was not complete. It consisted of alveolar-
columnar matter; its centre could not be made out.
This preparation also contained an example of Z'ylocephalum
minus.
The remainder of the pearls in Prof. Herdman’s collection, four
in number, appeared to be incomplete preparations, as no nuclei
or pseudo-nuclei could be observed.
D. Unlabelled Pearls (dry) in the British Museum,
In September 1911 Mr. E. A. Smith, 1.8.0., allowed me to
examine four dry pearls, from a small collection of pearls and
attached pearls and blisters, preserved in the Mollusca cabinets
at the British Museum.
These specimens were unlabelled and without history, but their
general characters (colour ete.) were those of J/. vulgaris, and the
fragments of shell to which some of them were attached were
undoubtedly referable to this species, and probably to examples
from Ceylon (heavily incrusted and much eorroded with Cliona).
Proc. Zoou. Soc.—1912, No. XXII, 22
[49j
338 DR. H. LYSTER JAMESON ON
Three of these pearls were decalcified, and one of them, Preparation
LXXXVIA, was also sectioned. All showed centres of the same
class as those of the pearls in Dr. Kelaart’s collection—that is to
say, central cavities containing irregular conchyolin-like strands
and a few granules. Two of these pearls were fair spherical
pearls, about 3mm. in diameter, which would have ranked as
‘“‘fine” pearls or ‘“* cyst-pearls,” b ae for blemished surfaces. The
third was a multiple pearl, secondarily attached to the shell, and
showed, by the presence of distinct traces of hypostracum in its
substance, that it bad arisen in a muscular part.
E. Collection of Pearls given to me by Mr. Max Mayer.
In April 1911, Mr. Max Mayer, of Hatton Garden, London,
and Paris, denies in precious stones, most generously gave
me for the purposes of my work a number of pearls, mostly
of the baroque and seed class (though some could better be de-
scribed as pearls that would have ranked as small “ fine” pearls,
but for defects of shape, colour, or surface). These included
a sample which, after eliminating a number of pearls that,
from their colour and other qualities, Mr. Mayer considered
were derived respectively from Australia and Panama (these will
be dealt with in another paper), left a mixed lot of 115 pearls,
most of which showed more or less of the characteristic and
indescribable creamy colour which is distinctive of the pearls
of Margaritifera vulgaris. Myr. Mayer had no hesitation in
saying that the majority of these were almost certainly Ceylon
pearls, though he emphasized the fact that it is not often that
pearls reach the European markets accompanied by “ certificates
of birth,” and that the sources of these specimens could only be
judged from their respective characters.
These 115 pearls were decalcified and eight of them were
sectioned, and several others were dissected to expose the
nature of the ‘“‘ nucleus” or pseudo-nucleus.
Of this collection not one had a nucleus that could be identified
as a Cestode, or indeed as any parasitic worm. Sixty of them had
spheerocrystal-like pseudo-nuclei composed of columnar repair-
substance, sometimes simple, sometimes stratified, sometimes
interstratified with other repair-substances. In some cases a few
granules could be detected in the centre, in others nothing of the
kind could be made out. These pseudo-nuclei were generally less
transparent than the residue of the pearl, often almost opaque
but in every case their nature was obvious. Forty-two pearls
were of the kind described from Dr. Kelaart’s specimens in the
British Museum, 7. e. they had either no obvious nuclei or their
centres contained cavities in which were a few strands of
conchyolin-like substance. Six others were of the same class, but
contained some refractive granular matter. One double pearl
showed a columnar pseudo-nucleus in one constituent and a
centre of the “Kelaart” type in the other, while another,
(80)
THE CEYLON PEARL-OYSTER, 339
a quadruple pearl, showed nuclei transitional between these two
types.
There remain the eight examples which had to be sectioned
to disclose the nature of their centres, owing to opaqueness. ‘The
first, Preparation XCIII, had a dark pseudo-nucleus which
proved to be composed of stratified amorphous substance, in fact,
a sort of horny pearl or periostracum-pearl. It was too hard
to section properly, and its real nature was discovered only
by dissection of the pseudo-nucleus. Preparation XCIV was
a triple pearl, and contained pseudo-nuclei of three kinds, a
* Kelaart” pseudo-nucleus, one composed of columnar substance,
and one composed of concentrically stratified amorphous substance
Preparation XCV had an irregular dark nucleus which in section
proved also to consist of stratified repair-substance, interstratified
with granules. In Preparation XCVI the centre was a hard
mass a columnar substance, coutaining a body that broke away
and may have been either amorphous substance or a hard body of
foreign origin. Preparation XCVITI contained a typical columnar
body, masked by a thick outer coat of amorphous substance.
The remaining three had pseudo-nuclei of ordinary columnar
substance.
I cannot say whether any of the above pearls contained
minute quartz-grains or other foreign inorganic bodies, as
this cannot be determined, even with the aid of polarised light,
in a great many eases, until sections are cut, owing to the high
degree of double refraction possessed by the conchyolin, and the
distortion of its original arrangement in the decalcifying process.
But such foreign bodies were detected in two pearls given to me
at the same time by Mr. Mayer, which were, however, more
probably from Margaritifera margaritifera var. mazatlanica
(Panama Shell) than from J/. vulgaris.
F. Collection of Ceylon Pearls given to me by
Mr. EB. Hopkins.
In October last Mr. E. Hopkins, dealer in precious stones, of
Hatton Garden, kindly gave me a parcel of fifteen small pearls,
which he believed to be Ceylon Pearls. He wrote me (letter of
26th October, 1911): “The pearls were obtained from a dealer
whose son visited the Ceylon Fisheries on the last occasion when
they were open, and from what he has told me I have every
reason to believe that these were part of the goods which he
brought back.” These fifteen pearls were decalcified and examined
as transparent objects, and four of them, which could not- be
satisfactorily made out otherwise, were subsequently sectioned,
Most of these pearls were of the « muscle- pearl” class, small and
angular, but two or perhaps three, both from their more spherical
shape and different nuclei or pseudo-nuclei, may more properly be
treated as parenchyma-pear!s.
Twelve of these pearls had centres of the kind characteristic of
29*
[81]
340 DR. H. LYSTER JAMESON ON
the pearls in Dr. Kelaart’s specimens, deseribed above, i.e. had mo
obvious nuclei, but simply central cavities containing either a few
irregular strands of conchyolin-like substance or obscure granules.
Two out of these twelve were sectioned. One, Preparation
Text-fig. 41.
lle ac
B.
A. Centre of a Ceylon pearl given to me by Mr. E. Hopkins. Decalcified and
examined whole in oil of cloves. Examined thus the body might be taken
for the remains of a Platyhelminthian parasite.
B. The same in section. The body is seen to be a “ pseudo-nucleus” consisting in
great part of amorphous substance, am., along with which is some granular
matter, g7. In the centre are some strange spore-like bodies, w, of doubtful
origin (Preparation LXXXV 1). X 400.
[82
THE CEYLON PEARL-OYSTER. 341
LXXXYV 4, had its central cavity lined with hypostracum, as in
the pearls described from the unlabelled specimens in the British
Museum. The other had a central cavity lined on one side by
a hilum-like plug of hypostracum, giving the pearl a reniform
outline, and on the opposite side by columnar substance, going
over into nacre. ‘wo of these muscle-pearls were composed of
several fused units.
There remain three pearls which have some claims to be treated
as parenchyma-pearls. One of these, which was not sectioned, had
in its centre a string of brownish granular matter, -66 mm. long
by -17 mm. wide, of doubtful origin (Preparation LXXXV 0).
Another (text-figure 41, A & B, Preparation LXXXV 1) had
a pseudo-nucleus *1 mm. in diameter, which, examined entire,
might have been taken for the remains of a minute Platy-
helminthian parasite, but which on section proved to be made
up in great part of amorphous repair-substance. Finally, one
peari (Preparation LXXXV xk), a round pearl just under 2 mm.
in diameter, possessing apparently all the external qualities
of a parenchyma-pearl, had for its centre a pseudo-nucleus of
stratified columnar substance, 1 mm. in diameter, surrounding
a sand-grain 35 mm, in diameter.
G. Pearls from Margaritifera vulgaris from the
Gulf of Kutch.
Being for the moment unable to obtain freshly preserved
material from Ceylon or Madras, I endeavoured to obtain examples
of the same species, preserved with pearls in situ, from Northern
India, and through the courtesy of His Highness the Jam Saheb
of Nawanagar, better known to most people in this country as
Prince Ranjitsinhji, I was supplied in October last with a valuable
collection of preserved oysters, containing pearls, from the
Nawanagar fishery. I wish here to record my indebtedness to His
Highness, and to Mr. Merwanji Pestonji, Dewan of Nawanagar,
for their help. My thanks are also due to Dr. G. A. Grierson,
C.1.E., Director of the Linguistic Survey of India, and to Mr. R.
KE. Enthoven, LC.S., for putting me in communication with the
Authorities of the State.
The detailed histological examination of this material will take
some time, but I have decalcified and sectioned a number of pearls,
free and in situ, for purposes of comparison with the material from
other sources.
As the Nawanagar fishery is littie known to biologists, the
following information, supplied to me by the Dewan, may be of
interest.
The fishery, which belongs to H.H. the Jam Saheb, is carried
on on the southern shore of the Gulf of Kutch, during the South-
West Monsoon season, from June onwards. The ground on which
the pearl-oyster is found is ‘* usually the sloping bank of a reef,
facing east or south-east, consisting of shingly sand and small
[83]
342 DR. H. LYSTER JAMESON ON
rocks and stones, clear of all mud.” Mr, Pestonji says that the
bottom of the sea around the reefs is muddy, and that it is
believed that the heavy rains and seas wash away the mud from the
Oyster-beds, and so make it easier to see and collect the oysters.
“At high tide there is usually about ten to twelve feet of water
over the Oysters. The oyster-beds are never dry, even at low
water, there always being an inch or two of water draining off” *.
The fishery is carried on by wading, at low tide. ‘‘ During the
Monsoon season four or five hundred men are sent out to a certain
reef, where they tramp about and pick up the oysters as they come
upon them. They stay three or four days on each reef, and when
one reef has been searched they move on to another. Each man
is rewarded according to the number and nature of the pearls found
in the oysters he brings in.”
The oysters are not * rotted,” as in the case of the Ceylon pearl-
fisheries, but are opened one by one, and the pearls removed “ by
scraping the flesh gently with a blade of a knife.”
The number of oysters fished annually is about 150,000, on
an average. ‘Ihe value is uncertain. The number of pearls
extracted from these oysters comes to about 20,000 and over.
They vary in size from seed- pearls to those weighing 20 grains and
over, The lustre and colour are of first-class order, but “the shape
in over 60 per cent. of the pearls is poor.
Mr. Pestonji estimates that if care is taken to pick up oysters
which are about four years old, about 10 to 15 per cent. of them
contain pearls. He says, in a letter dated November 14th, 1911:
‘“‘Lately we opened oysters three times. The first time we opened
643 oysters and got 452 pearls. The second time we opened
770 oysters, and got 537 pearls. The third time we opened 845
oysters, and got only 379 pearls.” Mr. Pestonji includes the
minute “ dust” pearls as well as pearls of different sizes and shapes
in this statement, and explains that there are often as many as
fifteen or more minute pearls in a single oyster.
Highteen pearls from this collection have so far been decalcified
and examined, and thirteen of these have been sectioned. Some
of these were sectioned in sitw in the tissues, others were pearls
which had fallen out of the tissues in the preserving process.
They differed in no recognisable microscopic features from the
pearls produced by the same species in Ceylon and the Persian
Gulf. Thirteen of these pearls, six of which were from one
specimen and three from another, were of the same character as
those described from Dr. Kelaart’s material in the British Museum,
that is to say, they had a small central cavity, surrounded by
ordinary nacre. The remainder had more or less obvious
pseudo-nuclei, composed of columnar or alveolar substance, in some
cases interstratified with nacre. ‘T'wo of these (Preparations
N. VII. and N. LX.) had nacre inside the columnar substance, with
* Spring tides rise 18 ft., and neaps 14 ft., aft Rojhi, an island near the town of
Nawanagar, according to the Admiralty Sailing Directions, “ West coast of
Hindustan Pilot ” (1898 edition).
[84]
THE CEYLON PEARL-OYSTER. 343
a central cavity, and their difference from the ‘“* Kelaart ” class of
pearls was therefore probably due to a difference in their secondary
growth, rather than in their primary origin. One of those
sectioned (Preparation N. IV.) had a pseudo-nucleus composed of
stratified columnar substance, with internally some nacre sur-
rounding a small mass of brownish granules.
It cannot, I think, be argued in comparing these pearls with
‘eylon pearls that they are all seed-pearls or “ muscle-pearls.”
They occurred in all the usual parts of the external body-wall and
mantle, and some of them had all the properties of small “ fine
pearls.” Preparation N. VI., for example, was a beautiful little
spherical pearl, of high quality, measuring about 2°5 mm. in
diameter, which I was extremely reluctant to sacrifice in the
interests of science, and a number of the others were solitary
“parenchyma-pearls ” of small size.
H. Two Pearls from Margaritifera vulgaris /rom the Mediterranean,
given to me by Professor Raphael Dubois.
Professor Raphael Dubois most generously placed at my
disposal for comparison two small pearls taken from J/. vulgaris
from the coast of Tunis. This species has firmly established
itself in several parts of the Mediterranean, since the opening of
the Suez Canal, having no doubt come through from the Red Sea,
either in the free-swimming larval stage or as young spat attached
to the bottoms of vessels. I can add nothing to what Dr. Dubois
has already said about the structure of these pearls, (8) pp. 103—
105. One contained a central body, rather less than °5 mm, in
diameter, which on being sectioned proved to be composed of very
homogeneous granular matter surrounded on one side by columnar
substance and on the other side by ‘amorphous substance.” The
other contained a small yellowish spherical body, ‘08 mm. in
diameter, which, examined in oil of cloves, showed no recognisable
structure. In section it appeared to consist of a very smal] amount
of granular matter, surrounded by what looked like st ratified
amorphous repair-substance. Dr. Dubois’s observations have
shown, without doubt, that the pearls produced by this species in
the Mediterranean (and their single occurrence, in positions away
from the muscle-insertions, renders it necessary to treat them in
part at least as Parenchyma-pearls and not as Muscle-pearls) have
not Cestodes in their centres, but have nuclei and pseudo-nuclei
similar to those which I have described above, for pearls from the
same species from other localities.
I. Pearls from M. vulgaris from New Caledonia, given
to me by Professor Seurat.
Professor L. G. Seurat, at my request, very kindly sent me four
small seed-pearls from Margaritifera vulgaris, from New Caledonia,
and also a slide, showing a larger pearl from the same species
[85]
344 DR. H. LYSTER JAMESON ON
decalcified and mounted entire in Canada Balsam. In none of
these could I find Cestode nuclei.
The example mounted as a slide was a pearl about 2 mm. in
diameter, of oval shape, from the Isle of Pines. It had two
pseudo-nuclei, side by side, both composed of columnar substance,
concentrically laminated. One measured *5 mm., the other
‘3mm. This pearl was subsequently sectioned, and no foreign
matter could be detected in the nuclei. I decalcified and examined
the other four pearls. The characters of three of them were
nearest to those of the pearls in Dr, Kelaart’s collection in the
British Museum described above, but one had several centres,
which were surrounded by columnar substance. The fourth had
a little brown body about -2 mm. in diameter, which sections
showed to be composed of unrecognisable granular matter
surrounded hyamorphous substance, No Cestode characters could
be identified in it.
M. Seurat also sent me five slides, with sections of pearls from
M. vulgaris from New Caledonia, which had been mounted in paraftin
wax, but had not been stained or made into finished preparations.
T stained and completed these, and found that they comprised
about seven pearls, in all of which, so far as could be determined
(for the series were not complete), the pseudo-nuclei were either
simple cavities containing a few granules or strands of conchyolin-
like matter, or masses of concentrically deposited, stratified
columnar substance. There was no trace of anything that I could
accept as a Cestode.
M. Seurat stated (37), p. 24, that these pearls had for nuclei
Cestode larve, but I am unable to confirm this. In a recent
letter he has informed me that this assertion was based on the
appearance of the nucleus of a decalcified pearl, which was not,
apparently, examined in section.
J. Pearl from M. vulgaris from Nossi-bé, Madagascar.
M. Seurat also sent me an unmounted slide with sections of a
pearl from this species from Nossi-Be. The centre of this pearl
was a mass of concentrically deposited columnar substance,
0-35 mm. in diameter, containing a cavity about 0-l mm. in
diameter.
K. Pearls from the Lapi Shell (M. vulgaris), from the
Trobriand Islands, Papua.
Prof. W. R. Dunstan, F.R.S., Director of the Imperial
Institute, very kindly allowed me to decalcify and examine two
pearls from this locality, which were taken from among those on
exhibit in the Papua Court at the Imperial Institute. These
specimens had recently been sent home, by direction of the
Administrator, the Hon. M. Staniforth Smith.
The pearl-banks occur on the western side of Kiriwina Island,
[86]
THE CEYLON PEARL-OYSTER. 345
and the fishery is carried on by the natives from whom the pearls
are bought by licensed traders. The annual yield is between £3000
and £4500 worth of pearls, as valued locally. The first of the two
pearls examined was decalcified by me, but was not sectioned.
The centre was a double pseudo-nucleus, slightly over a millimetre
in length, and a little under a millimetre in breadth. It was
obviously composed of stratified columnar substance. External
to this the pearl, which was quite a good one, was composed of
normal nacre.
The second example was decalcified and examined entire, and
then sectioned. The centre was a spherical pseudo-nucleus,
rather less than half a millimetre in diameter, also composed of
stratified columnar substance, with a minute central cavity, about
0-02 mm. in diameter.
These were certainly not “ Muscle” pearls, but small “ fine
pearls. The preparations have been returned to the Imperial
Institute.
”
L. Pearls from Placuna placenta, from Lake
Tampalakamam, Ceylon.
In view of Mr. Hornell’s statement, referred to in the account of
the work in Ceylon, to the effect that he had determined that a
Cestode larva, similar to or identical with that found in the pearl-
oyster, caused the pearls produced in such quantities by Placuna
placenta, the Window-pane Oyster, I thought that a study of this
form would throw light on the problem in J/. vulgaris. I made
several fruitless efforts to obtain material from Ceylonand elsewhere.
I examined one small pearl, decalcified and mounted whole, in
Professor Herdman’s collection (No. 78), labelled “ Pearl Shelled
from Mantle of Placuna.” This pearl measures about half a
millimetre in diameter, and the “nucleus” is a little yellowish
body, about ‘05 mm. in diameter, and thus too small to be Hornell’s
larva (which is said to be from *2 to ‘4 mm. in diameter), even if
it is of foreign origin. However, it was necessary to have
material to section before the matter could be investigated. As
I could not get other material Professor Dunstan very kindly
allowed me to take a few Placuna pearls from the collection on
exhibit in the Ceylon Court at the Imperial Institute. Two very
well marked size-groups occur in the pearls in this collection,
there being a majority of minute irregular pearls, 1 mm. in
diameter and under, and a minority of larger ones, averaging from
2 to 3 mm. in diameter, Prof. Dunstan allowed me to take
four of the latter and sixteen of the former. All these were
decalcified, and two of the larger and four of the smaller were
sectioned.
Of the larger pearls, Preparation CXLVI (sectioned) had for
its centre a cavity, ‘(05 mm. in diameter, containing a little
irregular columnar repair-substance. Preparation CXLVII had
a central cavity containing a small amount of yellow refractive
[87]
346 DR. H. LYSTER JAMESON ON
granular matter. The remaining two, which were decalcified but
not sectioned, had no obvious nuclei, the centres being, apparently,
like those of CXLVI and CXLVII. Of the sixteen minute
pearls four were sectioned. Preparation CXXXV_ had in its
centre a simple cavity, like the pearls in Dr. Kelaart’s material
of MW. vulgaris. Preparation CX XX VI showed a central cavity,
with around it some columnar substance, or perhaps hypostracum.
Preparation CXXXVII had a large dark pseudo-nucleus, over
half a millimetre long, which might easily have been taken for <
foreign body, when examined entire, but which on being sectioned
proved to be composed of concentrically laminated amorphous
substance, passing over in places into columnar repair-substance,
and containing a minute central cavity. Preparation CX XXVIII
had in its centre a little brown body, probably composed of
amorphous substance, but this specimen did not prove satisfactory
on being sectioned. The twelve remaining pearls were decalcified
and examined entire in oil of cloves, but were not sectioned. Of
these four had either a small central cavity, surrounded by
ordinary nacreous conchyolin, or no obvious nucleus or pseudo-
nucleus. Six had such cavities, partly or entirely surrounded by
repair substances or hypostracum, one had a few yellowish
granules in its cavity, and one had a dark body, about *3 mm. in
diameter, of doubtful nature, but showing no characters that
would warrant its identification as a Cestode.
The absence of evidence in support of Mr. Hornell’s Cestode
theory of the origin of Placuna Pearls is an additional argument
in favour of the opinion that the supposed observation of these
worms by Mr. Hornell and Professor Herdman in the pearls of
M, vulgaris was a mistake.
M. Pearls from Margaritifera margaritifera var. cumingil Reeve
(the Black-edged Mother-of-Pearl Oyster), from Likitea,
Gambier Archipelago.
In order to enable me to compare the pearls of M. vulgaris with
those of this species, in which Seurat claims that Cestodes occur as
nuclei, M. Seurat most generously placed at my disposal some
material. ‘This consisted of three slides on which sections of
pearls from this species had been mounted, but which had not
been stained or completed. I stained and finished these three
slides. In two of them the centre of the pearl could not be found,
in the third there was not a section through the exact centre, but
there was one that cannot have been far from it. This showed no
Cestode remains, but a pseudo-nucleus rather less than half a
millimetre in diameter, consisting in its more central part of
concentrically deposited columnar repair-substance, passing over
peripherally into alternate layers of amorphous and columnar
substance, which in their turn passed over into nacre, through
catenulated and granular transitional substance, such as I have
described in J. vulgaris.
[88 |
THE CEYLON PEARL-OYSTER. 347
M. Seurat also gave me a piece of the latero-dorsal region of
the body of this species, with pearls im situ. This I decalcified
and examined in oil of cloves, and afterwards sent to be sectioned.
At the time of correcting proof the sections had not been returned.
Examined entire in oil of cloves this specimen showed a cluster of
about ten pearls. Most of these were like those described from
Dr. Kelaart’s material of J. vulgaris, i. e., they had no obvious
nuclei; one, however, had in its centre a minute hypostracum
pearl or columnar pseudo- nucleus, about ‘1 mm. in diameter ;
one had a tiny refractive body, about ‘03 mm. in diameter, w hich
may have been composed of amorphous substance; and one had
some more opaque matter which, however, contained nothing that
could be identified as a Cestode.
It would seem possible, in view of these observations, that
M. Seurat may also have been led into the error of arguing that
because the ‘T'rematode which is associated with pearls in Mytilus
furnishes the stimulation necessary for pearl production, therefore
the Cestode in Margaritifera plays thesame role. I hope shortly
to receive further material from the French Pacific that will
enable me to go into this question more fully.
I may add that my studies on pearls from J/. maxima, and
from the other varieties of J/, margaritifera from other localities,
so far as these studies have gone up to the present, afford no
evidence of the occurrence of Cestodes in the centres of pearls.
(15) GENERAL SumMaRy.
The following are the principal conclusions to which these
investigations have led me :—
(1) The evidence that the globular Cestode larvee, which sha
Herdman regards as the cause of the formation of * fine pearls ”
the Ceylon Pearl- Oyster, are a young stage of the worm evanbed
by Shipley and Hornell as Tetrarhynchus unionifactor is quite
inconclusive. I consider these worms to be more probably
referable to the genus 7'ylocephalum (or an allied form), and have
provisionally described them under the name of Vylocephalum
ludificans and 7. minus, spp. nn.
(2) The theory that these Tapeworms are the cause or a cause of
the formation of pearls in the Ceylon Pearl-Oyster (in the sense
in which the Trematode is the “cause” of pearls in J/ytilus,
where the pearl-sac is normally formed as a result of the specific
stimulation of the worm) is supported by quite insufficient
evidence, and even their occasional occurrence in the nuclei of
Ceylon pearls has yet to be demonstrated *.
* Sir West Ridgeway, formerly Governor of Ceylon, Chairman of Directors of
the Ceylon Company of Pearl Fishers, Ltd., in reply to a question put, at the annual
meeting of Shareholders in 1909 (reprinted in the ‘ Financial News’ on December
2\st, 1909), as to what was known with regard to the real cause and mechanism of
pearl- formation, implied that the Directors were in possession of valuable informa-
tion, of a secret nature, on the subject. “It was most undesirable at this moment
that they [7. e. the Directors] should reveal the progress whicn had been made by
[89]
348 DR. H. LYSLTER JAMESON ON
It appears, in fact, as though the simultaneous presence of pearls
and Cestodes in the Ceylon Pearl-Oyster were a case of two parallel
diseases, comparable to the case of a dog infected simultaneously
with tapeworms and mange, or of a man suffering at the same time
from echinococci and scabies. And even should it be found that
tapeworms do sometimes form the nuclei of Ceylon pearls, an
explanation of the reason why this occurs in some cases only is
necessary. It is, of course, possible that in certain of the Ceylon
banks conditions may exist which cause 7'ylocephalum ludificans
to depart from its normal habit, and acquire an ectodermal instead
of a fibrous cyst; or it might even be found that in certain banks
another species of T'ylocephalum (or other Cestode) occurs which,
like the Trematode in J/ytilus, normally and habitually gives rise
to a pearl-sac in the tissues, and which has been confused with
Tylocephalum ludificans. But, in any case, pearls formed around
tapeworms, if such ever occur (and this still remains to be demon-
strated), must be so comparatively scarce that, from the economic
standpoint, the réle of the tapeworm in pearl-production in
Margaritifera vulgaris must be unimportant. Examination of
such pearls from Placuna placenta and Margaritifera margaritifera
var. cumingii as were obtainable failed to confirm the supposed
oecurrence of Cestodes as their nuclei.
(3) The shell of Margaritifera comprises in addition to the
hinge-ligament the same layers as those of other typical Lamelli-
branchs, viz. a periostracum (the outermost layer of which is
secreted in a different manner to the remainder and is very
much reduced in Margaritifera), prismatic substance, nacre, and
hypostracum or muscle-attachment substance,
In addition to these, certain pathological varieties of shell-
substance arise when the normal rhythm of secretion is disturbed,
the chief of which are described as amorphous repair-substance
(which is probably simply uncalcified conchyolin), columnar repair-
substance, and granular repair-nacre. These substances intergrade
with normal nacre and prismatic substance, and with each other.
The peculiar characters of these substances are the chief cause of
the distinctive appearance of the ‘‘ pseudo-nuclei” of pearls. The
shell-substance, except the hypostracum and the outer layer of the
periostracum (and probably the ligament), is secreted in liquid
form, and its structure and variation may be interpreted as the
expression of the normal processes of the crystallisation of CaCO,
in a colloidal medium, modified by the periodicity of the action
of the shell-secreting tissues of the mantle.
(4) The “Calcospherules,” which Herdman identifies as the
nuclei of muscle-pearls, are not free concretions or “ depositions
Mr. Southwell in his researches on this question; but he thought that gentleman
would support him in saying that those researches had not been unsuccessful up to
the present, and promised to be most interesting as well as satisfactory.” Mr.
Southwell’s thoroughly frank statements of the case in his subsequent publications
do not appear to me to reveal anything sufticiently epoch-making, from the com-
mercial standpoint, to render such mystery uecessary !
[90]
THE CEYLON PEARL-OYSTER. 349
from the blood” (Southwell), but are minute pearls formed
of the hypostracum or muscle-attachment substance. They are
therefore not the cause of the nacreous muscle-pearls, but a phase
parallel to them. There is some reason to believe that the origin
of muscle-pearls is associated with pathological invaginations
or immigrations of the epidermis at the points where the
muscle-attachment epithelium passes over into the ordinary
outer mantle-epithelium.
(5) Parenchyma-pearls (which name I apply to Prof. Herdman’s
cyst-pearls) may be formed around grains of sand or other foreign
particles, organic granular matter of doubtful origin, or bodies
composed of varieties of the shell-substance which arise when
the normal rhythm of secretion is disturbed (repair-substance).
A foreign nucleus is probably rather exceptional. The ultimate
factors which give rise to the epidermal sacs in which they are
formed have yet to be discovered. Many of them are probably
of the same origin as muscle-pearls, except that they arise singly
at points where a few muscle-fibres are inserted into the shell,
instead of in clusters at the regular muscle-insertions. The
dark pseudo-nuclei of these pearls, which may easily be mistaken
for the remains of parasites, are usually composed of the repair
substances.
(16) Works REFERRED TO.
(1) Brepermany, W. 1901.—Untersuchungen tiber Bau und Entstebung der
Molluskenschalen. Jenaische Zeitschr. f. Naturwiss. Bd. xxxvi. Hft. i.
pp. 1-164, Taf. i-vi. 1901.
(2) Brepermann, W. 1902.—Ueber die Bedeutung von Krystallisationsprozessen
bei der Bildung der Skelette wirbelloser Thiere, namentlich der Mol-
lusken. Zeitschr. f. allg. Physiologie, Bd. i. pp. 154-208. Jena, 1902.
(3) Bouran, L. 1903.—L’origine réelle des Perles fines. C.R. Acad. Sci., Dec. 14,
1903, t. exxxvil. p. 1073.
(4) Bouran, L. 1904.—Les Perles fines, leur Origine réelle. Arch. Zool. Expér.,
Sér. 4, t. ii. pp. 47-90. 1904.
(5) Buirscutr, O. 1898.—Untersuchungen tiber Strukturen. Leipzig, 1898.
(6) Birscrtt, O. 1908.—Untersuchungen tiber organische Kalkgebilde. Abhandl.
d. konigl. Gesellsch. der Wissenschaften zu Géttingen, Math.-Phys.
Klasse, Neue Folge, Bd. vi.no. 3. 1908.
(7) Dusors, R. 1907.—Sur un Sporozoaire parasite de ! Huitre perliére (Margari-
tifera vulgaris). Son Réle dans la Formation des Perles fines. C.R.
Soe. Biol. lxii. 1907, pp. 310-312. _
(8) Dusors, R. 1909.—Contribution a ?Etude des Perles fines. Annales de
VUniversité de Lyon, n. s., i. Sciences—Médicine, Fascicule 29. 1909.
(9) Enrenpaum, EK. 1885.—Untersuchungen tiber die Struktur und Bildung
der Schale der in der Kieler Bucht haufig vorkommenden Muscheln.
Zeitschr. f. wiss. Zool. Bd. xli. 1885, pp. 1-46, Taf. iii.
(10) Gtarp, A. 1903.—L’origine Parasitaire des Perles d’aprés les recherches de
M. G. Seurat. Comptes-rendus des Séances de la Société de Biologie
(Séance du 31 Octobre, 1903), t. lv. p. 1222. 1903.
(11) Hartey, G. 1889.—The Structural Arrangement of the Mineral Matters in
Sedimentary and Crystalline Pearls. Proc. Roy. Soc. vol. xlv. no. 279,
pp. 612-614.
(12) Harine, P. 1872.—Recherches de morphologie synthétique sur la production
artificielle de quelques formations calcaires organiques. Verhandl. d.
Kon. Akad. d. Vetenskapp. Amsterdam, Deel 14, 1872, 85 pp., 4 pls.
(13). Herpman, W. A. 1902.—Reports on the Pearl Fisheries of Ceylon.
Preliminary Report. Ceylon Sessional Papers, xii. 1902.
(14) Herpman, W. A. 1903.—Lecture delivered at the Royal Institution on
March 27th, 1903; Abstract in ‘ Nature,’ vol. 67, 1903, pp. 620-622.
[91]
350 DR. H. LYSTER JAMESON ON
(15) Herpman, W. A., & Hornett, J. 1903.—Note on Pearl-formation in the
Ceylon Pearl Oyster. British Association Report, Southport, 1903,
p. 695.
(16) Hernan, W. A. 1903-6—Report to the Government of Ceylon on the
Pearl Oyster Fisheries of the Gulf of Manaar. London: Published by the
Royal Society. 1903-6.
Part I. 1903.
Herpman, W. A.—Introduction and Narrative, pp. 1-98. —_»
= Fe Description of the Pearl Banks, pp. 99-121.
. PA Observations and Experiments on the Pearl Oyster,
pp. 125-146.
Part IT. 1904. Preface, pp. v—vii.
Hrrpman, W. A.—History of the Principal Pearl Banks, pp. 1-36.
“5 , Anatomy of the Pearl Oyster, pp. 37-76, pls. i—ix.
Surptey, A. E., & Hornet, J.—Parasites of the Pearl Oyster,
pp. 77-106, pls. i.-iv.
Part IIL. 1905. Preface, pp. v—viii.
Herpman, W. A. (based on Report and Letters of Mr. Hornet).
The Pearl Fishery of 1904, pp. 1-36.
. » (based on Report and Letters of Mr. Horne.n).
The Present Condition of the Pearl Banks, pp. 87-48.
Suiprey, A. E., & Hornety, J.—Further Report on Parasites, pp. 49-
56, plate.
Part IV. 1905. Preface, pp. v—vi.
Herpman, W. A.—The Great Pearl Fishery of 1905, pp. vii-xvi.
Part V. 1906. Preface, pp. i-viii.
Herpman, W. A., & Horyett, J.—Pearl Production, pp. 1-42,
pls. i-1ii.
SnuiptEy, A. E., & Horner, J—Cestode and Nematode Parasites
from the Marine Fishes of Ceylon, pp. 43-96, pls. i.—vi.
Herpman, W. A.—General Summary and Recommendations, pp. 109—
136, plate.
(16 2) Herpman, W. A. 1905.—Presidential Address delivered at the Anniversary
Meeting of the Linnean Society of London on 24th May, 1905. London:
Taylor & Francis, 1905.
(17) Herpman, W. A. 1906.—Address delivered at the Anniversary Meeting of
the Linnean Society of London on 24th May, 1906. London: Taylor &
Francis, 1906.
(18) Hesszive, TT. 1859.—Die Perlmuscheln und ihre Perlen. Leipzig, 1859.
(19) Hornett, J. 1905.—The Biological Results of the Ceylon Pearl Fishery of
1904. Reports from the Ceylon Marine Biological Laboratory, No. L.,
1905, pp. 1-39.
(20) Hornext, J. 1905.—Report on the November Inspection of the Ceylon
Pearl Banks, 1904. Ceylon Sessional Papers, xii., 1905.
(21) Horney, J. 1965.—Report on the Placuna Placenta Pear] Fishery of Lake
Tampalakamam. Ceylon Sessional Papers, xiv., 1905.
(22) Hornect, J. 1906.—Report on the Placuna Placenta Pearl Fishery of Lake
Tampalakamam. Ceylon Marine Biological Reports, Part II., June 1906,
pp. 41-44, plate.
(23) Hornets, J. 1906.—Report on the Inspection of the Ceylon Pearl Banks,
November 1905. Ceylon Sessional Papers, xvii, 1906.
(24) Huxuny, T. H. 1859.—Tegumentary Organs. 'Todd’s Cyclopedia of Anat.
& Physiol. vol. 5 (Suppl. Vol.). 1859,
(25) Jameson, H. L. 1902.—On the Origin of Pearls. Proceedings of the
Zoological Society, 1902, vol. i. pp. 140-166, pls. xiv.-xvil.
(26) Jameson, H. L. 1903.—The Formation of Pearls. Nature, vol. 67, pp. 280-2,
Jan. 22nd, 1903.
(26a) Jameson, H. L. 1912.—An Examination of the Causes which have led to
the Failure of the Biological work recently undertaken on the Ceylon
Pearl Fisheries. Journal of Economic Biology, vol. vi. pt. 1, pp. 10-22.
Feb. 1912.
(266) Jounsrong, J. 1912.—Tefrarhynchus erinaceus van Beneden.—I. Strue-
ture of the Larva and Adult Worm, Parasitology, vol. iv. no. 4,
January 8, 1912, pp. 364-415, pls. xix.—xxiv.
(27) Kevaarr, KE. H. 1857.—Introductory Report on the Natural History of the
Pearl Oyster of Ceylon. Trincomalee, 1857.
(27a) Linton, E. 1891.—Notes on Entozoa of Marine Fishes of New England,
with Descriptions of several New Species.—Pt. II. Report U.S.
Commission of Fisheries for 1887 [1891 |, pp. 719-899, pls. 1.-xv.
[92]
THE CEYLON PEARL-OYSTER. ao
(276) List, T. 1902.—Die Mytiliden des Golfes von Neapel. Fauna und Flora
des Golfes von Neapel: 27. Monographie. Berlin, 1902.
(27c) Mirsuxvrt, K. 1902.—The Cultivation of Marine and Fresh-water Animals
in Japan. Bulletin of the U.S. Bureau of Fisheries for 1904, vol. xxiv.
1905, pp. 259-289, pls. i.—x1.
(28) Moynrer De VritEporx, R. 1892.—Recherches sur la formation et l’accrois-
sement de la Coquille des Mollusques. Journ. de l’Anat. et dela Physiol.
t. Ixxviil., 1892.
(29) Mixer, F. 1885.—Ueber die Schalenbildung bei Lamellibranchiaten.
Schneider, Zoolog. Beitrage, Bd. i. Hft. iii. pp. 206-246, Taf. xxvili.—xxx.
(80) PagensrecuEer, H. A. 1858.—Uber Perlenbildung. Zeitschr. f. wiss. Zool.
Bd. ix. pp. 496-506, Taf. xx. 1858.
(31) ReaumeEr. 1709.—De la formation et de Vaccroissement des Coquilles des
animaux. Hist. de Acad. Roy. des Sciences; Paris 1711. Mém.
Anneé, 1709.
(32) Romer, O. 1903.—Untersuchungen iiber den feineren Bau einiger Muschel-
schalen. Zeitschr. fiir wiss. Zool. Bd. lxxv. Hft. iii. 1903.
(33) Russet, A. 1911.—Zur Kenntniss der Schalenregeneration bei der Fluss-
perlmuschel. Zoologischer Anzeiger, 7. Marz, 1911, Bd. xxxvii. Nr. 8/9,
pp. 169-172.
(84) Ruspen, A. 1911.—Die Entstehung der Perlen bei Margaritana margari-
tifera. Zoologischer Anzeiger, 25. April, 1911, Bd. xxxvii. Nr. 19/20,
pp. 411-416.
(84a) Russet, A. 1911.—Ueber Perlen und Perlbildung bei Margaritana
margaritifera nebst Beitragen zur Kenntniss ihrer Schalenstruktur.
Marburg, 1911. Pp. 80, two pls., and numerous text-figures.
(35) Seurat, G. 1904.—Sur la Biologie des Huitres perliéres et nacriéres des
Iles Gambier. C.R. Soc. Biol. tom. lvi. 1904, No. 7 (26 Février), pp. 294-295.
(36) Srvrat, G. 1906.—Sur un Cestode parasite des Huitres perliéres déterminant
la production des perles fines aux Iles Gambier. Paris, C.R. Acad. Sci.
tom. 142, 1906, pp. 801-803.
(87) Seurar, G. 1906.—La Nacreet la Perle en Océanie.— Péche.— Origine et Mode
de Formation des Perles. Bull. Mus. Oceanogr. Monaco, No. 75, 1906.
(38) Souruwett, T. 1910.—On the Determination of the Adult of the Pearl-
inducing Worm. Ceylon Marine Biological Reports, Part IV. pp. 169-172.
(89) Sovuruwett, T. 1910.—A Note on Endogenous Reproduction discovered
in the Larve of Tetrarhynchus unionifactor inhabiting the Tissues of
the Pearl Oyster. Ceylon Marine Biological Reports, Part IV., May
1910, No. 7, pp. 173-174.
(40) Sourawett, T. 1911.—Physical and Biological Conditions on the Pearl
Banks. Ceylon Marine Biological Reports, Part V., March 1911,
pp. 191-194.
(41) SouruweE t, T. 1911.—Further Notes on the Determination of the Adult
of the Pearl-inducing Worm. Ceylon Marine Biological Reports, Part V.
pp. 213-215.
(41a) Sovuruwett, T. 1911.—Description of Nine new Species of Cestode Para-
sites, including Two new Genera, from Marine Fishes of Ceylon. Ceylon
Marine Biological Reports, Part v. No. 18, pp. 216-225, plates. 1911.
(42) Sournwett, T. 1911—Some Notes on the Ceylon Pearl-inducing Worm.
Spolia Zeylanica, vol. vii. Part xxvul., May 1911, pp. 124-134.
(43) Srurnman, G. 1901.—Ueber die Bildungsweise des dunkeln Pigments bei den
Mollusken, nebst Bemerkungen tiber die Hntstehung von Kalkkarbonat.
Ber. naturf. Ges. Freiburg, Bd. xi. 1899-1901, pp. 40-45.
(44) Srempect, W. 1898.-—Beitrige zur Kenntniss der Nuculiden. Zool. Jahrb.,
Supplement-Band iv. : Fauna Chilensis, Bd. i. pp. 339-430, Taf. 22, 25. |
(45) Srempext, W. 1900.—Ueber die Bildungsweise und das Wachstum der
Muschel- und Schneckenschalen. Biol. Centralblatt, Bd. xx. Nos. 18-
22. 1900. :
(46) Turere, J. 1893.—Beitrage zur Kenntnis der Mollusken.—IT. Uber die Mol-
luskenschalen. Zeitschr. f. wiss. Zool. Bd. ly. 1893, pp. 220-250, Taf. xi.
(47) Tutieere, T. 1882.—Studien tiber den Bau und das Wachsthum des
Hummerparzers und der Molluskenschalen. Kongliga Svenska Vetensk.-
Akad. Handlingar, Bd. xix., No. 3, 57 pp., 12 Taf. 1884,
(48) Wirtey, A. 1907.—Report on the Window-Pane Oyster (Placuna placenta,
“Muttuchchippi”) in the Backwaters of the Eastern Province (June
1907). Spolia Zeylanica, vol. v. part xvii., Nov. 1907, pp. 33-56.
(49) Witrey, A. 1909.—Report of the Marine Biologist for 1908. Ceylon
Administration Reports for 1908, Colombo, p. G. 1.
(50) Lease of the Ceylon Pearl Fisheries. Ceylon Sessional Papers, x1., 1907.
[93]
ee)
On
Lo
DR. H. LYSTER JAMESON ON
(17) EXPLANATION OF THE PLATES
(The magnifications quoted are only approximate.)
PruatE XXXIII.
Fig. 1. Cestode larva (Tylocephalum ludificans or T. minus) in the act of migrating
through the tissues of Margaritifera v ulgaris. Drawn trom one of Prof.
Herdman’s shdes. The larva measured "12 mm. pa., parenchymatous
subepidermal tissue ; c.¢.f., connective-tissue fibres.
Fig, 2. Small larva, Tylocephalum minus, measuring ‘O8 mm., in the muscular
tissue of the mantle of MZ. vulgaris, without a surrounding connective-
tissue cyst. From one of Prof. Herdman’s slides. m.f., muscle-fibres in
cross-section ; ep., epidermis.
Fig. 3. Part of the fibrous cyst surrounding an example of the sinaller parasi.e
(Tylocephalum minus). In this case the parasite measured *O8 mm. in
diameter. J.¢., liver-tubules; 7./., inner, highly nucleated layer of the cyst.
x 800.
Fig. 4. Margaritifera vulgaris. Epithelial cells from the muscle-attachinent,
showing the connection between the cells and the muscle-fibres.
x 1000.
Fig. 4a. Margaritifera vulgaris. Muscle-attachment epithelium, showing cells
drawn out in fixation, and connective-tissue elements between their bases.
X 1200.
Proare XXXIV.
Fig. 5. Mytilus edulis. Section through the posterior adductor muscle-insertion
and decalcitied hy postracum. mus., muscle-fibres; hy., hypostracum,
which remains adherent to the muscle-attachment epithelium, ep. ;
hy.’, segment of hypostracum, corresponding to single epidermal cell;
nac., nacreous layers of the shell, which have torn away from the hypo-
stracum ; c¢., connective-tissue tibres, joining the muscle-fibres to the
attachment- epithelium. Preparation XXXIX. X 500.
Fig. 6. Margaritifera vulgaris, Persian Gulf. The part represented at A in
text-figure 35, showing the point of origin of a new lip-lappet of the shell.
1., 1.’, two suce cessively formed lappets. or marginal processes; pr., pr.’,
prisms of same; s.pr., s.pr.’, couchyolin-septa of the prisms; b.m.pr.,
conchyolin basal membrane of the prismatic substance of the first lappet ;
per., periostracum of the second lappet, which appears to be nothing
more than the outer conchyolin-membrane of the prismatic substance ;
point at which the second lappet arises from ‘the first, the peri-
ostracum of the seeond lappet being continuous with the basal
membrane of the first; y, irregular prismatic substance secreted at the
junction of the two lappets. Preparation X. x 300.
Fig. 6a. Margaritifera vulgaris, Persian Gulf. Decalcitied shell showing junction
between prismatic substance and nacre. pr., prisms; sep., conchyolin-
septa between same; sep.’, the same in surface view; anw., annular
thickenings of the septa; p7.b., basal conchyolin of the prismatic layer ;
con., connecting layer of alveolar conchy olin between the prisms and the
nacre; 2ac., nacre. Prepavation XI. xX 400.
Fig. 7. Margaritifer a vulgaris, Persian Gulf. “ Lingah Sheli” from London
market. Section ground from an old heavy shell. Portion of the adductor-
scar, showing the hypostracum, /iy., covered over in the direction of the
umbo by nacre, nae.’ ; nae., nacre underlying the muscle-scar, and secreted
before the muscle-attachment had moved to this place; hy.’, hy.'', extensions
of the hypostracum interstratified with nacre. Preparatica LXXYV.
X 120.
Puare XXXV.
Fig. 8. Muscle-pearl and hypostracum “cyst,” from the insertion of the posterior
pedal levator muscle of Margaritifera vulgaris. From a Ceylon specimen
given to me by Professor Herdman. The pearl is enclosed in a sac (which
has been ruptured by gas-bubbles in the decalcifying process), consisting
mainly of ordinary shell- secreting epithelium, bat lined at one pole with
muscle-attachment epithelium (m.ep.’). Opposite the ordinary epitheliam
L94]
THE CEYLON PEARL-OYSTER. aoe
the pearl consists of typical coats of nacre; but at the point where the sac
is lined with attachment-epithelium the pearl consists of hypostracum,
which also (or a substance analogous to it) lines the central cavity. Beside
the pearl, at ¢. is a cyst-like hypostracum-pearl, comparable to the lining
of the adjoining nacreous pearl. This hypostracum-pearl consistsof a cavity,
lined with hypostracum-like substance (yp.’), and on two sides it shows
muscle-attachment epithelium, m.ep.’’, but it has not acquired a lining
of ordinary nacre-secreting epithelium, and hence no nacreous coats
havearisen. ¢., cyst-like cavity of hypostracum-pearl; ep., shell-secreting
epidermis; ep.’, epidermis of pearl-sac; m.ep., muscle-attachment epidermis ;
m.ep.’, do. of pearl-sac; m.ep.’’, do. of hypostracum-pearl; m., muscle-
fibres ; pav., parenchyma; hyp., hypostracam which lines the muscle
pearl; hyp.’, do. of the hypostracum-pearl. Preparation IV,9. > 100.
Fig. 9. A muscle-pearl in the free mantle, froma slide in Prof. Herdman’s collection.
The area where the muscle-attachment epidermis is attached to the pearl
is relatively very small. The greater part of the pearl-sac is composed of
ordinary nacre-secreting epidermis, and consequently the pearl is enmposed
of nacre at all parts but one. o.ep., outer shell-secreting epidermis ;
i.ep., inner ciliated epidermis of the mantle-cavity ; par., subepidermal
parenchyma-cells, surrounding the pearl-sac; m.ep., muscle-attachment
epithelium, where hilum of pearl was attached ; muse., muscles of mantle ;
sac., pearl-sac; nac., nacre; rep.nac., granular repair-nacre, around central
part of pearl; hyp., hypostracum. X 70.
Prate XXXVI.
Fig. 10. An early stage of a muscle-pearl, from one of Prof. Herdman’s slides.
sac., pearl-sac; m., nacre; par., parenchyma; m., muscle-fibres; hyp.,
hypostracum-like cyst, around which the pearl is formed; m.ep., muscle-
attachment epithelium; c., a hypostracum-pearl. x 65.
Fig. 11. A ecyst-like hypostracum-pearl in the muscle-bundle, without any apparent
epithelial sac. From one of Professor Herdman’s slides. The cyst adjoins
the wall of a sac, ep.p.s.,in which a muscle-pearl was contained. hy.,
hypostracum; m., muscles ; par., parenchyma ; o.ep., outer shell-secreting
epidermis ; ep.p.s., epidermis of pearl-sac. X 400.
Fig. 12. Centre of the decalcified muscle-pearl which occupied the sac adjoining the
hypostracum-pearl shown in fig. 11. ¢., central cavity; g7.. granules in
central cavity ; ., nacre. X 500.
Fig. 13. Centre of a decalcified pearl, close to the mantle-margin, in one of Prof.
Herdman’s slides. c., central cavity; »., nacre; rep.n., repair-nacre with
radial reinforcements ; J.c., lining of the central cavity. > 300.
Prate XXXVII.
Fig. 14. Four pearls “in ovary” of Margaritifera vulgaris, from Dr. Kelaart’s
material in the British Museum. The pearls are close together as shown,
but their centres have been brought into the same plane in the drawing to
show the “nuclei.” Each pearl is surrounded by a mass of subepidermal
parenchyma, pay. ep., outer epidermis; ov., ovarian tubules ; m., muscle-
bundles. Preparation XX VII, 8. > 30.
Fig. 15. The centre of the pearl shown in the top left-hand corner of fig. 14.
¢., central cavities ; nw., nucleus-like matter, probably of the nature of
conchyolin, contained in same; 7vep.7., repair-nacre, with granular structure,
tollowing upon the cavity; 2., ordinary nacre of the pearl. Preparation
XXVIII, 8. > 400.
Fig. 16. The central portion of the pearl shown on Plate XLIV. fig. 48. »., central
«macre;, 2.’, peripheral nacre; c., central cavity; gr.d., granular layer,
causing the opaque yellowish appearance of the central mass.
Preparation LXXI s. xX 70.
Puate XXXVIII.
Fig. 17. A portion of the granular layer of the pearl shown in fig. 16, more highly
magnified. m., central nacre; .’, peripheral nacre; g7., granular layer,
‘suggesting dead cells; am.,am.’, two layers of amorphous horny substance.
Preparation LXXI gs. x 400,
Proc. Zoou, Soc.—1912, No. XXIII. 23
[95]
Bd4
Fig.
Fig.
Fig.
Fig.
Fig.
Fig,
DR. H. LYSTER JAMESON ON
18. The centre of the same pearl, consisting of a cavity, about ‘08 mm. in
diameter, surrounded by granular repair-nacre; the cavity contains a few
irregular strands or lamine of conchyolin-like substance, together with
certain granular bodies, possibly of cellular origm. Preparation LXX1 3.
x 450.
19. Group of muscle-pearls and hypostracum-pearls, from an old unlabelled
example of Margaritifera vulgaris in the British Museum. The centres
of the pearls have been brought into the same plane in the drawing.
The pseudo-nuclei range from ‘08 mm. to “15 mm. in diameter. At the
bottom and on the left-hand sides of the sketeh are two pearls with
eccentric pseudo-nuclei, in these eases composed of hypostracum,
showing that the nacre-secreting epithelium arose on one side of
the sac only. ‘The preservation does not allow of any histological
details of the tissues being shown. Four hypostracum-pearls are also
shown. mac., nacre; »v., coluramar pseudo-nucleus; nw.’, hypostracum
pseudo-nucleus, only partly surrounded by nacre; hy.p., hypostracum-
pearls ; mesc., muscle-bundles. Preparation XXWII, 4. X 380.
PuaTE XXXIEX.
g. 20. Centre of the pearl shown on the upper side of fig. 19. zac., nacre; col.,
colmmuar substance ; @m., amorphous substance; g7., granules in central
cavity. Preparation XX VII, 4. xX 350.
.21. A hypostracum-pearl, decalcified. gr., granules in central cavity; am.,
amorphous substance; hy. orgamic residue of the hypostracum.
Preparation XXVII,1. x 550.
21a.Part of a section ground through the middle of a hypostracum-pearl,
showing the columnar and stratified nature of its substance, and the small
central cavity. From an unlabelled specimen in the British Museum.
Preparation LXXVITI c. xX 70.
22. Portion of the mantle of Margaritifera vulgaris, near the margin, from a
second unlabelled specimen in the British Museum. Cleared in oil of
cloves, and examined entire before decalcification. ‘The specimen shows a
number of hypostraeum-pearls 7x situ. At rac. is seen a large hypostracum-
pearl in course of transformation into a nacreous pearl by the deposition
of nacreous layers around it. Preparation XXX. X 20.
x, 23. The same decalcified and examined in oil of cloves. mac., as above. X 20.
1G Geo) OU
24. A double nucleus, with abundant contents, from a pearl in the same
series of sections as figs. 19-21. gi., granular substance, apparently
derived from dead organic matter: a@m., amorphous cuticle-like layers;
am.’, « more deeply staining portion of the same substance, immediately
surrounding the granular contents of the nucleus ; col., columnar substance ;
nac., nacre. Preparation XXVIII, 7. > 250.
g, 25. A small hypostracum-pearl. Central cavity without contents. Preparation
XXVIL 11. x 100.
ig. 26. A double hypostracum-pearl, forming the nucleus of a naereous pearl.
am., (2) amorphous substance; fy., hypostracum ; hy.’, do. at periphery of
amorphous substance; nae., nacre; ac.’, columnar repair-substance.
Preparation XXVIII, 11. x 75.
27. Small pearl, with nacreous substance overlain by hypostracum. _ ¢., central
cavity, containing a few granules ; am., amorphous substance which passes
over into col., columnar substance; mac., nacre, which is succeeded by
hy., a layer of hypostracum, forming the outermost layer of the pearl.
This specimen shows well the difference between the reaction to stain
of hypostracum and the other substances, e. g. colamnar substance.
Preparation XXVII, 7. xX 350.
28, Pseudo-nucleus of the left-hand constituent of the double pearl shown in
fiz. 49 (Plate XLIV.). From one of the unlabelled specimens of
Margaritifera vulgaris in the British Museum. c., central mass composed
of (2) amorphous substance and granules; col., columnar substance ;
col.’, outer layers of the same, which pass over imperceptibly at one point
into nae.’, Nacreous substance; aec., complete layers of nacre around
nucleus; a., horny layer, probably composed of amorphous substance ;
96]
THE CEYLON PEARL-OYSTER. oa)
ceol.’’, incomplete columnar layer; nac.'’, nacreous substance of the pearl.
Preparation XLIII B. X 75.
Fig. 29. Margaritifera vulgaris, Persian Gulf. Portion of the repair-substance
formed inside the shell to close a large hole made by a borer of some kind
in the lateral region, below the umbo. am., amorphous substance ;
y, outer surface of repair-membrane; a, x’, cracks in the outer face of the
amorphous substance; col., columnar repair-substance; col.’, stratified
do.; tr., ¢r.’, transitional substance (granular repair-nacre) from columnar
repair-substance to nacre; nae., nacre. Preparation LXXVI. xX 400.
Vig. 29a. Margaritifera vulgaris, Persian Gulf. From a section through a blister
on the shelJ-margin, formed over a Leuwcodore tube. am., amorphous
repair-substance; alv., the same with alveoli containing carbonate of
lime; pr., prismatic substance. Preparation XI. > 500.
Pratt XLI.
Fig. 30. Margaritifera vulgaris; Dy. Kelaart’s material. Sections showing june-
tion between two of the constituents of a “multiple pearl,’ with the
various abnormal products which arose in association with the disturbances
caused by the fusion of the two pearl-sacs, and the retreat of the wedge-
shaped plug of tissue when its connection with its fellow of the opposite
side was broken down by the absorption or degeneration of the membrane
separating the two pearls. p., p.’, outer nacreous layers of the two pearls ;
rep.nac., gvanular repair-nacre; col., simple columnar substance, analo-
gous to that found im the nuclei of some pearls; am., amorphous
substance showing rough stratifications, perhaps corresponding to pauses
in the retreat of the wedge of tissue; ¢7., transition from amorphous
substance to columnar substance; ¢.’, transition from amorphous sub-
stance to granular substance; nac.’, nacre of the compound pearl embracing
both constituent pearls. Preparation LXXI c. X 300.
Fig. 31. Margaritifera vulgaris. Unlabelled specimen, British Museum. One end
of the suture between the fused-pearls shown in fig. 49, Plate XLIV.
nac., nac.’, the nacreous layers of the two pearls; col., col.’, columnar
substance, secreted after the epithelium had, through atrophy, lost its
power of producing nacre; ep., ep.’, the degenerated remains of the
epithelia of the pearl-sacs; par., the remains of the intervening paren-
chyma. Preparation LXIJI 3B. X 350.
Fig. 32. From the middle of the same suture; in this case the outlines of the
parenchyma-cells, par., are still visible. ep., remains of the epithelia of
the pearl-sacs. XX 350.
Fig. 33. Parenchyma-pearl in situ in the tissues of Margaritifera vulgaris, from
the Persian Gulf. _ep., outer shell-secreting epithelium ; ep.’. epithelium of
pearl-sac ; par., subepidermal parenchyma ; g/., gland-cells in same; musc.,
muscular coat ofthe visceral mass ; musc.’, musculature to wall of stomach ;
C.T., connective-tissue of visceral mass; ov., tubules of ovary; col., columnar
substance forming the centre of the pearl; xac., nacreous portion of the
pearl. Preparation LXIV B. x 80.
Fig. 34, Centre of a pearl from another example from the Persian Gulf. gr., granular
matter; am., (2?) amorphous substance ; nac., nacreous layer, immediately
surrounding the “ nucleus’; nae.’, outer nacre ; col.,columnar substance ;
col.’, imperfect layer of same, passing over laterally into nacre. Preparation
I MIVies 5O250)
Fig. 35. The central, spherocrystal-like pseudo-nucleus of the pearl shown in figs.
50 & 50 4 (Plate XLV.) ; from the sample of pearls purchased in Ceylon.
grnm., granular repair-nacre ; am., amorphous substance. Preparation
XLUI. x 400.
Prare XLT,
Fig. 36. The pseudo-nucleus of the pearl shown in fig. 52 (Plate XLV.); from series
purchased in Ceylon. g7., granular substance in central cavity forming
the true nucleus ; am., amorphous substance ; nz., pseudo-nucleus, which
here possesses a highly alveolar structure; co/., columuar repair-substance
passing over laterally into nae., nacre. Preparation LIJI. » 70.
Fig. 37. Alveolar columnar repair-substance and radially reinforced nacre, from the
pseudo-nucleus surrounding a sand-grain (or other hard body that broke
away) in a pearl from the same series. am., amorphous substance, forming
[97]
356 DR. H. LYSTER JAMESON ON
the innermost layer of the columnar pseudo-nucleus, col. ; nac., nacre
nac.’, radially marked, catenuiated variety of nacre, characterised by
radial rows of junctions which occur in small groups between conchyolin-
layers (june.); nac.’’, the normal nacre, passing over into this specialised
variety of nacre. Preparation LIV @. X 300.
Fig. 38. Tangential section through the alveolar-columnar substance shown at
col, in tig. 37. XX 300.
Fig. 39. Tangential section through the radially catenulated repair-nacre, shown at
nae.’ in fig, 87. june., the groups of junctions in radial rows, seen in
surface view. The section is near the inner surface of this layer. X 300.
Fig. 40. Centre of the imperfcetly decalcified brown pearl, shown in Pl. XLVI.,
fig. 57. nu., nucleus with rhombohedra of calcite ; am.’, lining of
amorphous substance; col., columnar layer; col.tr., transition-layer from
alveolar-columnar substance to amorphous substance; am., amorphous
substance, with scattered alveoli, containing calcium carbonate. Pre-
paration XL. X 280.
Fig. 41. Part of the same pearl, external to that shown on fig. 40, showing the
transition from amorphous substance, am., with scattered alveoli, through
an intermediate substance, ¢7., to needle-like prismatic substance, col.
xX 250.
Fig. 42. Transition from the needle-like prismatic substance, col., shown in fig. 41,
to the ordinary prismatic shell-substance, p., similar to that of the shell.
al., minute alveoli in the thickenings of the walls of the prisms, similar
to those observed by Rémer (82). X 2650.
i Pruate XLITI.
Fig. 43. A portion of the repair-substance in the body of a pearl, shown at col.
in fig. 386, showing transitions from amorphous substance to nacre.
nu., outer part of the pseudo-nucleus; am., amorphous substance, with
alveoli, which passes over into finely columnar substance, co/. This
in turn goes over through granular repair-nacre, g7., into normal nacre,
nac.’, and is followed by layers of normal nacre (nac.) externally. Pre-
paration LIT. x 400.
Vig. 44. Portion of the contents of the central cavity of one of the pearls purchased
in Ceylon; showing also a portion of the columnar substance which
surrounded the centre. The contents drawn are selected from a number
of the sections in the series cut from this specimen. ae., nacreous
substance of the pearl; col., columnar repair-substance surrounding the
nucleus; am.,am.’, anorphous substance; dia., diatoms; spic., fragments
of sponge-spicules ; veg., vegetable débris. Preparation LIV 3. XX 500.
Fig. 45. Fragment of a Radiolarian shell, from the centre of another of the same lot
of pearls. Preparation LIV 5. X 600.
PiatEe XLIV.
Figs. 46, 46 a. Pearl from a cluster of pearls in one of Dr. Kelaart’s specimens.
Decalcified and examined, 46, entire in oil of cloves, 46a, in section. The
diameter of the pearl was just 2 mm., that of the central denser part was
13mm. There is a simple central cavity. Preparation XVI. XX 27.
Figs. 47, 47 a. Another pearl from Dr. Kelaart’s material, decalcified and examined,
47, entire, and, 47 @, in section. The diameter of the pearl was 2 mm. ; that
of the dark, opaque, yellowish centre rather over 1 mm. Examined entire
the nucleus appears amorphous, and might well be mistaken for the dead
remains of a parasite; but this peculiarity was found, on sections being
made, to be due to a break in the continuity of the nacreous layers
and the interpolation of a dark layer, composed of irregularly calcified
conchyolin, and granules which are probably of extraneous origin. ‘There
is a small central cavity, as in the rest of Dr. Kelaart’s pearls, with a plug
of conchyolin-like substance at one side. g7., granular dead matter; col.,
columnar substance; 2, nacre. Preparation XV. X 27.
Fig. 48. A “double” pearl from Dr. Kelaart’s material, decalcified, cleared, and
examined entire. Sections through this pearl are shown on Plates
XXXVII. & XXXVIII. figs. 16-18. The pearl was 2°25 nm. in diameter.
The pseudo-nucleus was a dark opaque body, about 0° mm. in diameter,
similar to that shown in fig. 47, and might easily be taken, on examination
of the entire pearl, for the shrivelled remains of a dead parasite. Sections
[98]
THE CEYLON PEARL-OYSTER. 357
showed that here again the real nucleus was a cavity containing strands
or sheets of conchyolin-like substance and a few granular bodies, perhaps
of cellular origin (Plate XXXVIIL. fig. 18); while the dark appearance
of the central mass was due to the interpolation between the proper
poe layers ofan abnormal patholegical product. Preparation LX XI s.
X 27.
Fig. 49. A double pearl from one of the unlabelled specimens in the British Museum;
decalcified, cleared, and examined entire. The nucleus of the left-hand
constituent is figured on Pl. XL. fig. 28, the characters of the substance
at the suture between the two pearls at figs. 31 & 32 on Plate XLI. In
the pseudo-nuclei of these pearls the columnar substance is stratified.
Preparation LXIII Bp. X 27.
PLATE XLY.
Figs, 50, 50 a. The central portion of a white porcellanous spherical pearl, from the
sample of pearls purchased for me in Ceylon by the Ceylon Company of
Pearl Fishers, Ltd. Fig. 50, decalcified and examined whole in oil of
cloves. Here the nucleus, when examined whole, might well be mistaken
for a small Trematode. Fig. 50 a. Section through the centre of the same
pearl. The pseudo-nucleus is seen to consist of an irregular nacreous body,
shown in fig. 35 (Plate XLI.) to be granular repair-nacre, surrounding a
minute spherocrystal-like mass; about 0°08 mm. in diameter. Pro-
paration XLII. x 27.
Fig. 51. Another pearl from the same collection. An oval pearl, of fine quality,
35 mm. X 3mm. in diameter. This pearl shows a tract of stratified
columnar and granular repair-substance, extending outwards from the
pseudo-nucleus and passing over laterally inte the nacre, Preparation LI.
x 20.
Fig. 52. Another pseudo-nucleus, from a pearl in the same collection. This was a
small spherical pearl of fine quality, about 2 mm. in diameter. The
columnar substance here, ced., is alveolar in structure, and surrounds a
central cavity containing afew granules. Fora section of the centre of this
pearl, see fig. 36 (Pl. XLII.) Preparation LIT. X 27.
Figs. 53, 53a. Centre of another pearl from the same series. The pearl was oval,
about 3 mm. in diameter, with a faint zonar constriction and a rather
coppery tint. Examined entire (fig. 50) it shows a large pseudo-nucleus,
over a millimetre in diameter, which falls into three layers. It also shows
a blemish in the nacre, coated over with repair-substance. Fig. 53 @
shows the same in section, The columnar repair-substance is finely
reticulated or alveolar. The blemish is caused by a few granules, which
have found their way into the pearl-sac and have been covered over with
columnar repair-substance, which passes over laterally into ordinary nacre,
Preparation LIV. X 27.
Figs. 54,54 a. Fig. 54. Central portion of another pearl, which measured about
3mm. X 2°75 mm. A pearl of fine colour, but with slightly irregular
surface. The nucleus of this pearl is a sand-grain, enclosed in an opaque
yellowish coat, probably consisting of repair-substance, At one pole is
seen a process of repair-nacre, but, except for this, no columnar substance
appears to surround the grain. Vig. 54a. The sand-grain, dissected out
from the above preparation. Preparation LIT. ™X 27.
PratE XLVI.
Fig. 55. Fine spherical pearl, from the same series, about 2 mm. in diameter.
Nucleus a grain of sand surrounded by a thin layer of columnar substance,
thickened at one pole. Preparation LIV mw. xX 27.
Fig. 56, Another pearl from the same series, a small spherical pearl about 2 mm. in
diameter. ‘The nucleus is a grain of sand, forming the centre of a typical
pseudo-nucleus of columnar substance. Preparation LIV a. X 27.
Fig. 57. A brown pearl, spberical, 3 mm. in diameter, formed of the prismatic
substance. From thesame collection. xw., pseudo-nucleus; co/., columnar
substance ; am., amorphous substance; co/.’, fine columnar-prismatic sub-
stance ; pr., ordinary prismatic substance ; 4/., blister formed over intrusive
foreign matter. For the several substances of this pearl, more highly
magnified, see Plate XLII. figs. 40-42. DPreparation Xl. X 27.
Ss.
[99]
358 ON THE CEYLON PEARL-OYSTER.
Kig. 58. Tylocephaium ludificans, sp.n. Type. Section through an example in the
tissues ot the Ceylon Pearl-Oyster in Professor Herdman’s collection.
Slide 94 of Professor Herdman’s series. a., armature of collar. This shows
the myzorhynchus of “ Tylocephalum” form, due to the posterior face
(m.p.) being contracted and its surface thrown into folds and the anterior
tace (m.a.) stretched. Compare the adult 7'ylocephala in figs 61 & 62,
and also the species shown in fig. 65. X 70.
Fig. 59. Section through another example of the same species, showing the “ Cepha-
lobothrium’’-form of myzorhynchus; here the posterior surface of the
myzorhynehus (m.p.) is tense, and its anterior surface (7.a.) is thrown into
folds. a, armature of collar. (Compare theadult worm in fig. 66.) X 70.
Fig. 60. An adult worm, which may be the adult of Tylocephalum ludificans,
from the spiral intestine of Aétobatis narinari. X 6. From Dr. Shipley’s
collection.
Puate XLVIL.
Fig. 61. The head of the worm shown in fig. 60, viewed as a transparent object.
m., myzorhynchus ; s,s’, s’’, three of the four marginal suckers; a., armature
of collar ; seg., first proglottides. XX 70.
Fig. 62. The same, in section; letters as above. XX 70.
Fig. 63. Armature of collar of same, about point @ in fig. 62. XX 1000.
Fig. 64, Penultimate segment of same.
Fig. 65. Head of Tylocephalum uarnak from Trygon uarnak. From a slide in
Dr. Shipley’s collection. my., myzorhynchus, which here is fully protruded ;
ma., anterior face of same; mp., posterior face; s, s’, s’’, s’’’, the four
marginal suckers. X 45.
Fig. 66. Head of Cephalobothrium aétobatides from Aétobatis narinari. From a
specimen in Dr. Shipley’s collection. Letters as above. X 70.
[100]
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