104 CEYLON PEARL OYSTER REPORT. 



Fig. 12. Another larva of the same stage, seen under slighter pressure, and higher magnification, x 40 

 diameters. The vertically striated mucilaginous cuticle is clearly shown, together with a net- 

 work of anastomosing vessels. Cut., cuticle ; Ex. p., excretory pore. 



,, 13. Shows the beginning of the change from a spherical to an elongated form of body. Taken from 

 a cyst from the viscero-pedal mass of the pearl oyster. 



,, 14. Portion of same larva seen in optical section at region of proboscis collar, showing a fragment of 

 the anastomosing network of vessels and the large bladder-like cells full of clear globules, lying 

 beneath the dermal layer (semi-diagrammatic). The calcareous corpuscles are omitted for the 

 sake of clearness. Den., denticles ; Par., sub-dermal bladder-like cells ; Pr.sh., proboscis sheath ; 

 /"'*-., anastomosing vessels. 



,, 15. a. Optical section of body- wall of a Cestode larva from the pearl oyster, showing the normal 

 appearance. /'. Final stage, when, under continual pressure, the mucilaginous cuticular layer 

 has disintegrated, its place being taken by one or two layers of the bladder-like cells, which 

 thus come to invest the body of the larva, c. Tho same as a under slight pressure ; an 

 invasion of the delicate cuticular layer by bladder-like cells full of clear globules is in progress, 



PLATE II. 



Fig. 1C. Forms of the calcareous corpuscles found in the larvae of Tetrarhynchus unionif actor. 

 17. The same, enclosed in the cells that secrete them. 

 ,, 18. Form of denticles which ornament the proboscis collar of the early larva of Tetrarhynchus 



UMonifactor. 

 ,, 19. The oldest larval stage of Tetrarhynchus unionifactor met with in the tissues of tho pearl oyster. 



Arm. cil., armature of stiff cilia around excretory pore; cs., one of the two pairs of cephalic 



suckers; Ex.v., external orifice of excretory system ; Pr., protractile proboscides; Tr.ex., lateral 



trunks of excretory system. 

 ,, 20. Surface view of the posterior extremity of the same individual on an enlarged scale. 



a. Shows the warted pattern of the whole surface of the body, except at the extreme 



posterior extremity, where, as shown (b), the surface marking becomes sinuous ; other letters 



as in fig. 19. 

 21. A loop of the excretory network in the cephalic region of the same individual. 

 22. Anterior extremity of an individual of the same stage as that depicted in fig. 19 seen under 



greater magnification. Pr.sh., sheath of proboscis ; Eet.m., retractor muscle of proboscis. 

 ,, 23. One of the hooklets from a proboscis. 

 24. A larval form of Tetrarhynchus balistidis from the liver of a Batistes, sp. x 16 diameters. 



C.c, calcareous corpuscles; Tr.ex., excretory trunks. The natural size is shown by the small 



figure to the right. 

 25. Sub-spherical larva of Tetrarhynchus balistidis found in oval and in rounded cysts beneath the 



peritoneum of Batistes, sp. ; Pr.pro., proboscis protruded. 

 ,, 26. A slightly older example of the same. 



27. Natural size of a cyst of T. balistidis from abdominal cavity of a Batistes, sp. 

 28. Cyst from peritoneum of Batistes, nat. size, containing T. pinnas. 

 ,, 29. The larval T. pinnce freed from cyst membrane. Nat. size. 

 Figs. 30, 31, 32. The same, under higher magnification. C.c, calcareous corpuscles; Cy. mem., cyst 



membrane; Pr.ret., proboscides retracted ; Sc, scolex. 

 Fig. 33. Teeth of T. balistidis, isolated by maceration and highly magnified. 

 ,, 34. Teeth of T. balistidis in situ on the introvert. 

 ,, 35. More teeth of T, balistidis for comparison with fig. 36, 



