226 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



satisfactory instance is recorded of the cestode parasite being 

 observed surrounded by an epidermal sac " (Proc. Zool. Soc, 1912, 

 p. 273). It has been still more doubtful whether the larval intruder 

 ever developed within a cyst, or within a pearl into the adult 

 worm, whose proper final host was the devourer of the oyster. 

 The precise identity of the worm or worms and the host in 

 tropical waters are still unknown ; but evidence has recently 

 been found of a pearl containing the complete remains of what 

 was supposed to be a fully developed worm within its nucleus. 

 This pearl was sectioned, as shown in Fig. 8 (PI. VIII), and the 

 section revealed under the microscope the figure of the letter S. 

 After the section was sent for a magnified photograph the lower 

 bend of the S was found to have disappeared. Later, unsuspicious 

 of danger, the same process was repeated, with the result that the 

 upper part disappeared, leaving barely sufficient for identification 

 of actual vermian remains. This disaster is undoubtedly attributable 

 to heat engendered in the jDhotographic process, but the original 

 figure was seen by Dr. G. T. Prior at the Natural History Museum, 

 as well as by others, one of whom asserted he saw the "horns" and 

 tail — and he unhesitatingly picked out Fig. 70 on Plate IV of " The 

 Parasites of the Pearl Oyster ", by Sir Arthur Shipley, as of similar 

 appearance. Fig. 70 represents the head and " horns " of the 

 adult Tetrarhyncus minimus, but having regard to Figs. 19 and 22, 

 representing the " oldest larval stage of Tetrarhyncus imionif actor, 

 met with in the tissues of the pearl oyster ", there is no certainty 

 as to the specimen found being actually a fully developed worm. 

 The similarity also between T. minimus and T. unionifactor in the 

 " horns " renders precise identification from memory uncertain. 



EXPLANATION OF PLATE VII. 



Blister Pearls from Pinctada [ = Meleci,grina\ maxima (Jameson). ■ 



Fig. la, h. Natural blister (nat. size) containing a stray shell. 

 ,, 2a, b, „ „ „ „ Pinnoteres. 



„ 2c. „ „ ( X 3) 



Reproduced by kind permission of Mr. A. Lanburn. 

 „ 3a, b. Natural blister (nat. size) containing a pearl. 

 „ 4a, 6. „ „ „ formed in the lower valve as a defence 



against the intrusion of a shell-boring bivalve. 



EXPLANATION OF PLATE VIII. 



Sections of Culture and Natural Pearls. 

 Fig. 5. Section of artificially produced blister from Japanese pearl oyster 

 {Pinctada martensii, Dkr.), sold largely hitherto as " Culture 

 Pearls " and utilized as half-pearls in cheap jewellery. 



„ 6. Magnified section of a 5 grain Japanese culture pearl (Jin. in diam.) 

 containing a mother-of-pearl bead centre. 



,, 7. Magnified section of Australian pearl (:|in. in diam.) in a shell blister. 



„ 8. Magnified section of Australian pearl (2^ in. in diam. min.) of dull 

 surface, showing removal of a number of skins by a linife on the 

 straight side for the purpose of testing the quality of the skins 

 below. 



