84 Drs. Kelaart and Mobius on the Natural History of the 



and terminates, as I have just remarked, on the side opposite to 

 where the mouth is placed. There is always an unclosed space 

 between the edges of the mantle, when the tentacles are brought 

 together, admitting of the free passage of excrementitious mat- 

 ter ; and it was through the same opening between the mantle, 

 that I observed, on one occasion, the ova escape, in a cloudy 

 stream which continued to pass into the water for nearly fifteen 

 minutes. I failed to detect the immediate part of the animal 

 through which the ova found their exit ; and I have not been 

 able to detect a regular oviduct. The ovaria, when distended 

 with ova, cover nearly the whole of the stomach, heart and liver, 

 and project even on the conical csecal process of the stomach, 

 and also on the base of the foot. The stomach is very small, 

 placed in the centre of the liver; the oesophagus is very narrow, 

 scarcely admitting a moderate-sized probe ; it is about 3 lines 

 long. The mouth, situated near the hinge, behind the foot and 

 byssus, is a horizontal slit, of about 3 lines in length, in the 

 duplicature of the lower pair of labial palps. These palps are 

 large, broad, truncated anteriorly, and rounded on the sides ; 

 the inner surface plaited, or rather grooved. The sense of feel- 

 ing or touch is, no doubt, by this rugose structure, greatly in- 

 creased. The palps serve the animal as organs of touch, if not 

 of taste ; they also serve to collect food, and give the animal the 

 power of rejecting indigestible particles of matter, or such sub- 

 stances as might prove injurious." 



The food of the Pearl Oyster, according to Dr. Kelaart, con- 

 sists of minute Algae, Infusoria, and Foraminifera. Diatomacece 

 and other microscopic organisms are found growing abundantly 

 on the outer surface of the shell ; " so that the oyster may be 

 said to carry on its back the food upon which it lives." 



The Pearl Oyster of Ceylon is of small size, the shells usually 

 measuring only 2^-3 inches in their largest diameter; but it 

 nevertheless takes six or seven years in reaching maturity. Like 

 our Common Oyster, it appears to have the sexes distinct ; at 

 least, although the majority of the specimens of all ages are 

 found to contain ova, a few are met with bearing " spermatozoa 

 or seminal fluid, in organs similar to those which, in a larger 

 number of individuals, contain ova." Even the native divers 

 are of opinion that there are male and female Pearl Oysters ; 

 and Dr. Kelaart justly states that "the important part which 

 the male oyster must play in the formation of banks of oysters 

 is self-evident, if it can be clearly established that the ova 

 absolutely require the vivifying influence of a male fluid," or, 

 tather, that this fluid is always secreted in the sexual organs 

 of male individuals. At the same time he observes, that he has 

 not seen more than three or four individuals with this milky 



