20 CEYLON PEARL OYSTER REPORT. 



fig. 11), by Pintner, in 1903, and is quite consistent with the section of a 

 Cysticercus of Tetrarhynchm given by Moniez in his ' Essai Monographique sur 

 les Cysticerques,' at plate hi., fig. 1, and with Pintxer's figure of Tetrarhynchus 

 smaridum (' Sitzb. Akad. Wiss., Wien.,' Jahrg. 1893, Abth. I.). 



The hooks (Plate III, figs. 2 and 9) are similar to those shown by various authors 

 as belonging to different larval Cestodes. The spines upon the projecting annular 

 pad or collar are, for example, rather like those of Twnia (Devainea) frontina, 

 Dujardin ; and Pintner shows a very similar arrangement to what we figure, in his 

 ' Studien liber Tetrarhynchen.' III., Taf. i., fig. 6. 



The calcareous corpuscles are not seen so well in the preserved specimens from 

 which the sections have been made in Liverpool as they were in the fresh material 

 we examined in Ceylon, but there can be little doubt that it is the remains of these 

 bodies that we show along with the loose network of connective tissue in the vesicle 

 behind the invagination in figs. G, 7 and 8 on Plate III. 



The division of the more opaque (? muscular) tissue in the scolex at the bottom of 

 the cup cannot be seen distinctly in all specimens, but the appearance shown in 

 Plate II., figs. 19 and 20, can scarcely be interpreted otherwise than as the beginning 

 of the segregation to form four discs (or bothridia) with their proboscides. 



The possession of all these characters together, in our opinion, definitely stamps 

 the organisms as larval Cestodes. It is no easy matter, however, to refer these 

 larvae to their proper genus. We find later stages in the tissues of the pearl oyster 

 which clearly belong to Tetrarhynchus, in a wide sense, but it is difficult to find 

 conclusive evidence that these younger larvae belong to the same organism as the 

 later forms with four proboscides. Giard is of opinion that Setjrat's similar figures 

 represent a member of the group Monobothria in the order Pseudophyllidea. 

 Seurat gives as his later opinion, as we have shown above, that they belong to a 

 new species of Linton's genus Tylocephalum. In either case the terminal invagina- 

 tion would represent a sucker with a papilla on its floor. We are inclined to 

 regard it rather as the opening in a hood or depression formed by the sinking 

 of the scolex into the front of its vesicle. The changes of shape which we 

 observed in this larva in the living state, the protrusion and retraction of the 

 papilla-like part which we regard as the anterior end of the scolex, agree with this 

 interpretation. Consequently, we are of opinion that this larval Cestode is not 

 one of the Monobothria that it belongs to neither the Pseudophyllidea nor the 

 Tetraphyllidea, but is a young Tetrarhynchid belonging to the Trypanorhyncha, and 

 we give here (fig. 4) a series of diagrams in order to show the positions that we 

 suppose our stages to occupy in the development of such a form. 



In regard to the life-history of the pearl-inducing parasite, we have little to add to 

 what has already been published in the preceding parts of this Report. In the 

 Introduction (Part L, p. 12) an outline of the history was sketched which still holds 

 true in the main. Shipley and Hornell in Part II. (p. 77) described and figured 



