CANTON^ ON PARASITIC OVA. 43 



sembling each other, as may be seen, e. g. in Monostoma 

 verrucosum infesting the fox, in T(snia cyathiformis belonging 

 to the swaUow, and in Tcenia variabilis of the gambet. In 

 some cases, where the filaments are shorter, the eggs more 

 closely resemble those to which you have directed my atten- 

 tion. This is evident in the ova of a curious trematode — 

 Octohothrium lanceolatum — attached to the gills of the com- 

 mon herring, and likewise in the eggs of the still more eccen- 

 tric-looking parasite — Polystoma appendiculata — found on the 

 branchige of various marine fishes. 



" In all probability, the entozoon from which the ova you 

 have found proceed is closely allied to those forms of trematode, 

 or fluke-worm parasites, whose eggs display only one thread- 

 like appendage, or ' holdfast.^ For example, the eggs of 

 different species of Dactylogyrus infesting the gills of the 

 pike exhibit ova of this kind (a good representation of this 

 is given by Guido Wagener in ' Siebold and Kolliker's Zeit- 

 schrift,^ vol. ix, plate v, fig. 8). The eggs of Diplozoon pa- 

 radoxum are also especially worthy of notice, a's, from G. 

 Wagener's recent Prize Essay {' Beitrage zur Entwicklungs- 

 geschichte der Eingeweidewiirmer'), it would appear that the 

 single filament is liable to vary in length ; whilst (as Van 

 Beneden, Dujardin, and other observers have shown) the 

 end of the filament is ordinarily coiled upon itself in a man- 

 ner precisely analogous to that noticeable in the ova from the 

 eye of the turtle. 



" On the whole, therefore, I think we may safely conclude 

 that the ova under consideration are referable to a parasite 

 more or less allied to the well-known Diplozoon paradoxum 

 of Nordman ; and I have little doubt that — if not already 

 known to some Continental helminthologist — we shall, ere 

 long, discover them in the oviducts of some species of Poly- 

 stoma, Tristoma, Octobothrium, Dactylogyrus, or other allied 

 genus of trematode worm." 



