April 1, 1903.] THiE TROPICAL AGRICULTURIST. 709 
for example, in the great Australian motlier of- 
pearl oyster, Margaritifera maxima, Jameson, 
black leathery pearls are sometimes found in the 
dorsal body-wall. I next proceeded to investigate 
the ^ 
ORIGIN OF THli SAC IN WHICH THE PEARL 
ARISES, 
and also the nature and origin of the " nucleus" 
which is so often to be found in the centre of the 
pearl. In a great many molluscs, among which 
were several of the pearl-oysters proper, the 
remains of trematodes were found to from the 
nuclei," a discovery which confirmed the observa- 
tions of Filippi, Mobius and others. In one or 
two cases, however, other parasites played the 
same part. By confining my attention to the 
common mussel, I proved that the epithelial sac, 
which is all-important for pearl formation, is first 
formed around the live trematode which enters 
upon a resting stage in the tissues of Mytilus. A 
similar sac, surrounding a trematode, was found 
in an example of the Ceylon pearl-oyster, 
Margaritifera vulgaris, Schumacher, which I 
examined. For the formation of the pearl, it is 
not necessary for the trematode to persist as 
nucleus, for it often happens that it migrates 
out of the sac ; but the sac, caused primarily by the 
specific stimulation of the parasite, is essential to 
pearl production. In Mediola mediolus, and prob- 
ably in some other forms, similar sacks are 
formed around Sporozoa. The next subject to be 
investigated was the origin and 
LIFE HISTORY OF THE PARASITE THAT CAUSES 
THE I'EARL-SAC. 
The common mussel was found to be the most 
convenient species on which to study this, and 
the pearl-bearing mussel-beds of Billiers, in 
Britany, and Piel, in the Bariow Channel, were 
selected as suitable sites in which to begin the 
observations (Fig. 2 ) The parasite, like most 
trematodes, passes through a regular cycle of 
three hosts, two of which are invertebrates and 
the third a vertebrate. It arises in sporocysts in 
the " tapestry shell," Tapes decussatus and the 
cockle Cardiuinedule, the former acting as first 
host at Billiers, the latter at Piel, where Tapes 
does not occur. The young tail-less Cercarite or 
trematode larvse leave the mother sporocysts in 
the first host and migrate into the mussel. The 
transmission of the parasite from Tapes to Mytilus 
was proved experimentally in a tank at the 
Brighton Aquarium. In the mussel, the parasite 
enter.'' into a resting stage, in the sub-epidermal 
connective tissue, and gives rise to the epidermal 
sac or " epithelioma " in which the pearl arises 
(Fig. 3.) If the parasite dies in this sac, a pearl 
is formed around its remains, or if it migrates 
to another part of the tissues, a pearl may be 
• eveloped in the empty sac; Although it was 
found impossible to secure live uninfected material 
of the final host for experiment, it is almost 
ceitain that the adult stage of the parasite is 
Distoma (Leucithodendrium) somateriw, Lev,, a 
whom which occurs in the intestine of the elder 
duck, Somateria moUissiiyia, and the black duck 
or scoter, Ocdemia nigra. Both these birds 
feed almost exclusively on mussels. A number of 
scoters caught or shot in the immediate viciu'.ty 
of the Billiers pearl-beds were found swarmiog 
with this worm. Indeed, one example of the worm, 
in an Immature condition, quite indistinguish- 
able from the restinf^ stage which occurs in 
Mytilus, was taken from the intestine of a scoter. 
Our knowledge of the life-stories of other tre- 
matoders, or " flukes " as they are popularly 
called, enables us to fill in the life history of 
this parasite with considerable detail. The 
worm reaches maturity iu the intestine 
of the scoter and eider, and the eggs 
pass out with the fceces. These eggs, or 
possibly "Miracidium" larvje derived from them, 
enter Tapes or the cockle and there give rise to 
sporocysts, in which the young Hukes or Cercarise 
are formed. These larvte, unlike typical Cercarise, 
are tailless, and when they escape from Tapes 
reach the mussel chiefly by drifting with the tidal 
currents. On entering the mussel, they pierce 
the body wall and settle down in the subcutaneous 
tissues, iu which they become surrounded by the 
pearl-sacs. If the mussel lives long enough, pearls 
will be formed in these sacs. If, on the other 
hand, a mussel containing these resting Cercaria; 
is eaten by an eider duck or scoter, the Cercarife 
develop into the mature worms, which produce 
eggs, and the life cycle is repeated. As an 
ECONOMIC RESULT. OF THESE IN VESTIQATIONSf 
it would seem that the artificial production of 
marketable pearls in large quantities should pre" 
sent no great difficulties, if the conditions essential 
to pearl production in the particular cases be 
intelligently investigated. The fact that trema- 
todes have been ascertained to be at least one 
causes of pearl formation in several of the molluscs 
that produce the marketable gems gives us every 
reason to hope that, by learning the life- histories 
of these parasites, we may be able to infect any 
number of pearl-oysters of pearl-mussels to any 
desired extent, without any operation on the 
individual molluscs, by simply placing them 
in the roper surroundings, in company with 
infected examples of the first host. Once 
infected, the molluscs could be bedded out on 
suitable grounds, and left to care for themselves, 
until the pearls formed in them were of market- 
able size. 
FUTILITY OF OYSTERS TRANSFERENCE,' 
These observations show the futility of the 
proposal that has so often been made, viz., that 
young pearl oysters should be transferred from 
their native grounds to more accessible in-shore 
waters, as it must obviously be the first object 
of the scientific expert, before laying down the 
beds of young peail-oysters, to assure himself 
either that they are already infected or that 
the conditions essential to speedy infection are 
present on the grounds to which the oysters are 
to be transplanted.— H. Lyster JAMESON in 
Nature, Jan. 22. 
— ^ ... ^ 
The Cacao Crop of Trinidad— is expected to 
be very large this season. The Poi-t of Spain 
Gazette estimates tiiat during the month of De- 
cember, close upon 20,0tX) bags (of 130 lb each) 
will have been brought down by the railway. 
The Grenada Si. George's Clironi'cle draws atten- 
tion to the necessity of supplementing the cacao 
industry with others, in view of the rapid increase 
in cacao production in other parts of the world. 
The export of this crop from West Africa has 
risen from 166.054 bags in 1898 to 297,054 bags 
in 1902. From South America also increased pro- 
duction is recorded. Bahia for instance exported 
192,000 bags in 1900, and 236,546 bags in 1902 
Agricxdtiiral New Felj. 14. 
