PEARL PRODUCTION. 41 



Fig. 5. Nucleus of a decalcified cyst pearl from the posterior ear-region of a Cheval Paar oyster, showing 



the characters of the Cestode larva, x 20. 

 6. Partially calcified cyst around a dead Cestode larva, from the mantle of a 3-year-old Muttuvaratu 



Paar oyster, x 20. 

 7. Nucleus of a decalcified cyst pearl from the mantle of a Cheval Paar oyster, showing a Cestode 



larva with a spherical calcification in its interior, x 20. 

 8. Young Cestode larva (Tetrarhynchus unionifactor}, extracted from thick-walled cyst in mantle of 



pearl oyster, x 40. 

 9. Young Tetrarhynchus larva, extracted from a cyst in the mantle, showing the spines upon the 



" collar." x 40. 



10. The same, seen after slight pressure has caused the evagination of the " head." x 40. 

 11. Another slightly later stage, seen under slight pressure, x 60. 

 12. Rather later stage of the larva, showing elongation of body ; from a cyst in viscero-pedal part of 



pearl oyster, x 30. 



13. Encysted later larva of Tetrarhynchus pinnce. x 10. 



14. Later larva of Tetrarhynchus pinnce, freed from the cyst-membrane, x 10. 

 15. Late larva of Tetrarhynchus balistidis. from the liver of the File-fish, which eats pearl oysters. 



Natural size, and " head " x 16. 



16. The latest larval stage of Tetrarhynchus unionifactor met with in the pearl oyster, x 30. 

 17. Part of the liver of the pearl oyster, showing one of the smaller (A) and one of the larger (B) 



Cestode larvae encysted in the connective tissue, x 50. 



18. Globular larval Cestode encysted in the connective tissue of the liver, x 300. 

 19. One of the smaller larvae (Tetrarhynchus sp.) surrounded by a very thick connective-tissue cyst, 



showing a laminated structure, x 50. 

 20. Larva in the same stage, showing the division of the muscle masses into incipient bothridia, or 



proboscides. x 300. 



21. Another larval stage, surrounded by a dense connective-tissue cyst, x 300. 

 22. Another similar larva, slightly younger, showing a very slight cyst, x 450. 



PLATE III. 



Fig. 1. Section of larva of Tetrarhynchus unionifactor, showing an unusually depressed head, x 300. 

 2. Section of another larva, showing the usual protruding papilla, x 960. 

 3. An oblique section, x 40 showing the developing muscular tissue at a enlarged. 

 4. Another oblique section, showing lateral muscular thickenings, x 40. 

 5. Section through a larva, showing infoldings on the head, x 40. 

 6. Section of the usual form, with large muscular protruding head, x 40. 

 7. Posterior end of the last section, showing details, x 300. 



7A. Details of the fibres and spines on the cuticle of the last, more highly magnified. 

 8. Typical longitudinal section through the larva of T. unionifactor as seen commonly encysted in 



the pearl oyster, x 960. 

 9. Group of hooks in situ from the cuticle on the anterior invagination of the larger Cestode larva 



(T. unionifactor) ; with enlarged outlines of two isolated hooks, x 1000. 

 10. Section through a very young Tetrarhynchus, with the four proboscides ; from cyst between 



stomach and liver in pearl oyster, x 50. 

 11. Section through more elongated Tetrarhynchus, also from a cyst in situ in the viscera of the 



pearl oyster, x 50. 



G 



