T. Southwell 
33 
(3) Taeiiiura melanospilos. Adult specimens of Tetrarhynchus 
herdmani only, found in the spiral valve. This fish was an enormous 
specimen measuring seven feet six inches. 
(4) Ginglymostoma concolor. Adductor muscles of oysters found 
in stomach. Thirty-eight specimens of Tetrarhynchus unionifactor in 
one specimen (1910) after 31 days in the enclosure, and fifty-one speci¬ 
mens in another (1909) which had lived in the enclosure 28 days. 
These results are full}" described in Parts IV and V, Ceylon 
Marine Biological Reports. The point that immediately concerns us, is, 
that of the fish tried the only one suitable for the experiment was 
Ginglymostoma concolor. That the various fish placed in the enclosure 
had been eating oysters vigorously, was witnessed by the fact that the 
bottom of the enclosure was littered with fragments of broken shell. 
I was enabled to actually see the extent of these depredations by 
means of the diving dress. Although specimens of this fish had 
previously been examined no specimens of Tetrarhynchus unionifactor 
had ever been obtained from them. It is therefore almost certain 
that these Cestodes were derived from the oysters eaten. Otherwise 
it would be difficult to account for their presence in this fish on 
two successive occasions, and their absence from the same species 
of fish—as in every other species of fish examined—direct from the 
open sea. 
It is further to be remembered that during the time the experiments 
were being conducted, oysters were practically absent from the banks, 
and the only specimens obtainable were scattered specimens found 
growing on reefs, and in which pearl-inducing larvae were exceedingly 
rare. I have no doubt in my own mind that if a similar experiment be 
repeated when oysters are common on the banks, the results will be 
made absolutely couclu.sive. One seems justified therefore in saying 
that these specimens of Tetrarhynchus unionifactor were derived from 
the larvae inhabiting the tissues of the oysters eaten, and that 
the life history of the parasite is direct from the oyster to the final 
host. 
During 1907 I had numerous opportunities of examining the pearl- 
inducing larvae found in Placuna placenta (the window oyster) occur¬ 
ring in the backwaters at Trincomalee on the east side of Ceylon. This 
larva is exactly similar to that of the pearl-inducing worm of the pearl 
oyster. As we have already noted, Willey pointed out that this larva, 
found in Placuna, multiplied in an endogenous manner. During a visit 
to Tamblegam in September, 1911 I examined a few specimens of 
Parasitology v 
3 
