8 



Society, that purpoi'ted to show the remains of cestodes in 

 the centres of pearls, were capable of other interpretation. 

 Moreover, he could not find in any of the pearls sectioned by 

 Prof. Herdman, numbering some twenty-five or more, which 

 Prof. Herdman had kindly allowed him to examine, a single 

 instance of a cestode larva forming the nucleus. This observation 

 was borne out by the results of the examination of between 300 

 and 400 pearls from Margaritifera vulgaris, mostly from Ceylon, 

 but also comprising examples from the Pex-sian Gulf, the Gulf 

 of Cutch, the Mediterranean, Madagascar, New Caledonia, etc., 

 none of which, on decalcification, showed cestode or other platy- 

 helminthian larvas as nuclei. The centre of such a pearl was 

 (where it consisted of material other than the nacre or other 

 normal constituents of the shell) nearly always composed of an 

 abnormal form of shell-substance, analogous to that formed to 

 repair an injury to the shell, which, owing to its opacity, might 

 easily be mistaken for a foreign body. 



These i-epair-substances were sometimes associated with granular 

 matter, the origin of which was obscure ; this matter might 

 perhaps be derived from the tissues, or might possibly be of 

 parasitic origin, but Dr. Jameson saw no reason for regai-ding it 

 as derived from a cestode larva. 



Dr. Jameson regarded the presence of these cestodes as a 

 disease parallel to, but independent of, " margarosis " ; and 

 compai'ed the case of a pearl-oyster, containing both cestodes 

 and pearls, to that of a man suffering simultaneously from 

 echinococci and scabies, or of a dog infested at the same time 

 with tapeworms and mange. 



The author then discussed the systematic position of these 

 cestode larva;. Prof. Herdman regarded them as a younger 

 stage of a Tetrarhyncluis larva, which also occurred in the pearl- 

 oyster, and which, acting on this assumption, Shipley named 

 Teti'arhynchus unionif actor. The adult of this worm occurred 

 in the Ray {Rhinojitera ^avanica). Here, again, the author 

 maintained that two parallel forms were confused, and that the 

 larva which Herdman thought to be the cause of pearls was 

 not a younger stage of Tetrarhynchus unioiiif actor, but a species 

 referable to TyJoceplialum or some allied genus. He had found 

 a worm which might be the adult of this larva in the Ray 

 {Aetohatis narinari). This supposed pearl-producing larva, and 

 a similar smaller one, also found in the Ceylon Pearl-Oyster, were 

 described as new species under the names Tylocephalum ludificans 

 and T. minits. 



Prelwiina7'y Descriptions. 



Tylocephalum ludificans, sp. n. 



The worm svipposed by Prof. Herdman to be the cause of 

 "fine" pearls in the Ceylon Pearl-Oyster. Globular resting 

 scolex, with conical, flattened, or concave myzorhynchus, 



