May 2, 1904.] THE TROPICAL AGRICULTURIST. 751 
gill?, liver, and mantle of tbe pearl oyster ; and 
liave traced later staj^es through thebody of the oys- 
ter and in the peritoneal membrane of the Balistes. 
But it is not sufficient for the oyster to be infected 
by the Tetrarhynchus larva. It must also live, 
retaining its parasite, until such time as it can 
produce sufficient deposit of the calcareous secretion 
to entomb the living source of irritation, which 
thus becomes the nucleus of a pearl. This history 
is discussed more fully on some preceding pages, 
and the Cestode parasite will be described, along 
with the other parasites of the pearl oyster, in a 
special section of the report. The cysticercoid cysts 
of the Tetrarhynchus larvre are frequently very 
abundant in the liver of the pearl oyster. In the 
case of some paars, the Muttuvaratu especially, 
.scarcely any of the individuals examined are free; 
we have counted eleven encysted larvre in a sin- 
gle liver. In the gill, filaments and in their mem 
branous bases also they are common, while in many 
cases the mantle is infested. The gonads, the foot, 
and the palps all occasionally harbour the parasite. 
The muscles are the only large organs where the 
cysts are rarely found. In one individual oyster 
Mr Hornell made out a total of forty-five cysts for 
all the tissues. It may he well to repeat here that 
the Gestoi^e parasites are not ooly common, but 
are also apparently very widespread and generally 
distributed ; that Balistes with its parasite occurs 
both at Trincomalee and at Galle as well as in the 
Gulf of Mannar ; and that, in short, there can be 
no doubt as to the probable infection of pearl 
oysters grown at these or any other suitable loca- 
lities around Ceylon. 
The results of our cruises in the " Lady Have- 
lock," detailed in the " Narrative,,' showed clearly 
the advantages of dredging both as a method of 
exploring and surveying the banks and also for 
the purpose of raising large quantities of oysters 
from the bottom in a short time. Worked from a 
handy sea-worthy vessel, of Uie type of a large tug, 
or a modern steam trawler with a steam winch 
near the stern, the dredge -becomes in practised 
hands an instrument of precison, and will bring 
up a fair sample of everything on the ground, 
including the bottom deposit. Moreover the opera- 
tion is a speedy one. A line of soundings and 
dredgings can be run over a very considerable 
area in one day's work, and a much larger and 
more continuous, and therefore more represen- 
tative, sample obtained than would be possible 
by diving. From such a steamer, on the occasion 
of a fishery, four dredges at least could be worked 
simultaneously, as in the case of the steamer 
"Pyefleet" employed by the Corporation of 
Colchester in dredging "native" oysters in the 
estuaiy of Colne. There need be no fear that 
dredging, operations would be destructive to any 
young oysters that may be mixed with the old, or 
would in any way damage the ground os an 
oyster paar. Dredging is tlie usual practice on 
oyster beds in Europe and America. 
Our results on tlie "Lady Havelock" showed 
that neither young nor old brought up by the 
dredge are injured, and it would be a simple 
matter on the steamer to separate the young and 
return them to the water or iran=iport then to 
otiier ground; while it would be very difficult, if 
not impossible, to get this done in the divers' boats 
under present conditions. 
On several occasions, as shown in the "Narra- 
tive," we found by dredging considerable numbers 
of pearl oysters on spots not recognised as known 
"paars. " I feel confident, from the nature of the 
ground and our knowledge of their conditions 
(such as currents and the free-swimming stage of 
the young pearl oyster), that new deposits of spat 
must make their appearance from time to time at 
new localities, and may appear any time on some 
grounds outside the recognised paars, and all such 
new beds will probably remain unknown unless 
discovered by dredging traverses across the whole 
oyster-bearing plateau of the Gull of Mannar. At 
several localities we examined the ground outside 
the known paars down to the 100 fathom line, with 
the view of ascertaining whether there is any 
evidence in support of statements which have 
sometimes been made to the efl'ect that there were 
probably unknown beds of pearl oysters further 
out and in deeper water, from which spat was 
produced for the supply of the inshore paars. 
No such evidence was obtained. All fresh spat 
which has appeared in the past, after grounds have 
been cleared by fishing, must then have come 
from other beds of adulb oysters upon the plateau 
within the 10-fathom line — beds which have re- 
mained unknown and unfished. 
In addition to beds of adult oysters which may 
in this way be found by dredging traverses, it must 
be remembered that newly-established deposits 
of young oysters upon unsuitable ground where 
they cannot mature will be certainly made known 
from time to time, and this will give the material 
for re-planting the paans recently cleared by a 
fishery. Our experiments showed that young 
.oysters are more easily transported than older ones, 
and move readily re-establish themselves on new 
ground. 
In regard to the fish-trawling operations, I have 
to report that the greater part of thePalkBay 
presents a large open expanse with a uniform soft 
bottom suitable for trawling. Our hauls in both the 
north and the south parts of the area showed that 
there are plenty of fish, and apparently this shallow 
sea serves as a very valuable nursery for young 
sea-fish. We also found off Galle, to the east 
of the Callehogalle bank, at a depth of 25 to 30 
fathoms, an area which may be regarded as a fish- 
nursery. Here it is evident that the young of both 
flat and ronnd fish, belonging to about ten species, 
and including such valuable forma as ' Soles,' 
•Turbot' and 'Plaice,' congregate in large 
numbers. 
It would naturally be part of the duty of a 
Marine Biologist to the Colony to make himself 
acquainted with the conditions of the native 
fisheries, and be prepared to advise as to whether 
facilities should be given for introducing trawling 
in suitable localities, or whether any regulations 
are required for the protection of the nsh-nurseries. 
As an example of an accessory investigation snc'n 
as would be undertaken by the Marine Biologist, I 
may note that during our visit in Februaiy, 
1902, to Trincomalee we found the commercial 
sponge living in the bay. I asked Mr Hornell to 
return later in the year and look into the matter. 
He did so in October, and was very successful in 
determining ihe localities and mode of growth of 
the sponge, which is the true Euspo.igia officinalis, 
and very similar to the Mediterranean form. 
Professor Deudy, the sponge specialist, who has 
examined san^ples for me, thinks well of the 
quali'.y, and says " the possibility of establishing 
a sponge- fishery is worth consideration." 
For the proper carrying out of work in 
Ceylon it was found necessary to fit up the 
