286 UIl. 11. l.YSTEK JAMESOX OX 



stivge. (The fact that the undoubted Tetrarhi/nc/ii in the pearl- 

 oj'ster occur in and around the digestive canal suggests that 

 they follow the normal course and are swallowed in the egg-stage, 

 and first hatch out in the intestine of the oj^ster.) Mr. South- 

 well states (Oeylon ]\[arine Biological Repoi^ts, Part IV. No. 6, 

 p. 169, 1010) that this free-swinimiug larva has not been seen 

 since it was first discovered (see also 42, p. 127). 



I may here mention that one of Prof. Herdman's slides which 

 1 examined shows an interesting phase in the biology of these 

 supposed pearl-inducing Cestodes which may have escaped him. 

 It shows a small Cestode, 0"12 mm. long, with myzorhynchus and 

 collar fully developed, clearly in the act of passing through the 

 tissues. This may possibly represent the young of either form, 

 when first entering the oyster, or it may be a case of voluntary 

 or accidental migi'atiou by Tylocephaliun mintts (PI. XXXIII. 

 fig. 1). Dr. Willey (48, p. 50) records a similarly free larva seen 

 moving about in the liver of a species of Venus. 



To return to the life-histoiy of the true TetrarhyncJms vnioni- 

 factor, Shipley and Hornell have shown without doubt that the 

 adult sexually mature worm occurs in the Ray, Rhinoptera javanica 

 (Herdman's Report V. Cestodes, pp. 65-66). The identification 

 of the final host as jRhinoptera jai-anica is announced by Mr. 

 Hornell in a postscript to his Report on the November Inspection 

 of the Pearl Banks, 1904 (20, p. 8). Mr. Southwell (42, p. 130) 

 gives Tcemura melanospilos as another host. 



Professor Herdman in his Royal Institution Lecture, and in 

 Pt. I. p. 12 of his Report, claimed the File-fish, Bcdistes, as an 

 intermediate host ; but Shipley and Hornell, in Herdman's Report, 

 Part II. p. 83, say that " a more minute examination, however, 

 renders the connection between the parasites of the pearl-oyster 

 and those of the file-fish a doubtful one " ; and the immature 

 TetrarliyncM found in this fish are described as distinct species 

 under the names of Tetrarhynchns hcdistidis and 7'. phuice-. Prof. 

 Herdman sums up the position in the article on Peai-1-Production 

 (Report V. p. 24) by saying : — 



" No fresh light has been thrown upon the possible 

 occurrence of an immature stage in Bcdistes (which is eaten 

 by the large rays), :ind although that intermediate host may 

 not be necessary to the life-history, since the rays also feed 

 upon pearl-oysters, still there is nothing in the observed facts 

 to forbid the existence of such a stage, and it is not unusual 

 in Tetrarhynchids to have two fish-hosts, an intermediate 

 Teleostean which is devoured by a final Elasmobranch." 



Mr. Southwell's subsequent investigations confirm Prof. Herd- 

 man's view that Bcdistes occurs as a collateral intermediate host 

 or "carrier"; he says (42, p. 132):— "It is certain that my 

 encysted Tetrarhynchns ttnionifactor from Bcdistes is not the 

 same species as those described " (/. e. by Sliipley and Hornell 



