( s ) 
will be dealt with in full in the final report. I have also thought it well to defer, until our specimens 
are fully worked up, my remarks upon the marine biology in general and upon the trawl fisheries 
and other marine industries upon which biology has a bearing. 
The leading points in the conclusions I have come to in regard to the pearl oysters of the Gulf 
of Mannar may be summarized as follows : — 
(1) The oysters we met with seemed on the whole to be very healthy. 
(2) There is no evidence of any epidemic or of much disease of any kind. 
(3) A considerable number of parasites, both external and internal, both Protozoon and 
Vermean, were met with, but that is not unusual in molluscs, and we do not regard 
it as aflPecting seriously the oyster population. 
(4) Many of the larger oysters were reproducing actively, 
(.1) We found large quantities of minute " spat " in several places. 
(6) We also found enormous quantities of young oysters a few months old on many of the 
Paars. On the Periya Paar the numloer of these probably amounts to over a hundred 
thousand million. 
(7) A very large number of these young oysters never arrive at maturity. There are 
several causes for this : — 
(8) They have many natural enemies, some of which we have determined. 
(9) Some are smothered in sand. 
(10) Some grounds are much more suitable than others for feeding the young oysters, 
and so conducing to life and growth. 
(11) Probably the majority are killed by overcrowding. 
(12) They should therefore be thinned out and transplanted. 
(13) This can be easily and speedily done, on a large scale, by dredging from a steamer, at 
the proper time of year, when the young oysters are at the best age for transplanting. 
(14) Finally, there is no reason for any despondency in regard to the future of the pearl 
oyster fisheries, if they are treated scientifically. The adult oysters are plentiful on 
some of the Paars and seem for the most part healthy and vigorous ; while young 
oysters in their first year, and masses of minute spat just deposited, are very 
abundant in many places. 
To the biologist two dangers are, however, evident, and, paradoxical as it may seem, these are 
overcrowding and uverfi&ldng. But the superabundance and the risk of depletion are at the opposite 
ends of the lite-cycle, and therefore both are possible at once on the same ground, — and either 
is suEBcient to cause locally and temporarily a failure of the pearl oyster fishery. What is required 
to obviate these two dangers ahead and ensure more constancy in the fisheries is careful supervision 
of the banks by some one who has had sutBcient biological training to understand the life-problems 
of the animal, and who will therefore know when to carry out simple measures of farming, such as 
thinning and transplanting, and when to advise as to the regulation of the fisheries. 
I have, &o., 
W. A. HERDMAN. 
No. 2. 
Sir W. 0. TWTNAM, K.C.M.G., to Hon. Mr. R. W. Ibvers, C.M.G. 
Alfred Villa, 
Jaffna, June 30, 1902. 
Dear Mr. Ibvers,— Tour letter regarding the pearl oysters on the Cheval bank. Captain 
Donnan has, I presume, told you all that can be said at present regarding them in his report of the 
last inspection. The oldest oysters on the bank were about 3^ years old. They ranged from 3, to 
3^ in March last. I was with Captain Donnan when he picked up the simples for Professor 
Herdman in October last. I joined him in March last only after the inspection of the Cheval and 
Moderagam had been made, and therefore the only opinion I can form of them is from what Captain 
Donnan told me and from the samples he had on board. Of coarse there was nothing like an 
inspection of the banks in October, Captain Donnan having only gone to them to pick up samples 
from sections of the banks for Professor Herdman. We were on the banks only three working days, 
and anchored on five different spots some distance from each other, viz. : — 
Four on Cheval bank : southern part of East Cheval ; centre West Cheval ; north of 
West Cheval ; north of East Cheval. 
One on Moderagam bank, viz., centre of North Moderagam. 
From all the patches we anchored on the diver brought up oysters from eighteen months to 
three years old lying, according to his report, thick on the banks. He brought up 20, 40, 80 at a dive, 
and in two dives on the North-West Cheval he brought np 100. 
Except at our anchorage on the north of East Cheval, the diver reported the ground and the 
old oysters thickly covered with young oysters from minute spat to four months old. They were 
lying, according to his report, in myriads on the bank. Numbers of them were brought up adhering 
thickly to the old oysters. On one oyster there were as many as 65. 
