GYRODACTYIilD^. 



45 



of peculiar hooks projecting from the posteriorly- situated sucking 

 disk. In the aberrant genus Galceostoma, this mechanism is reduced 

 to a siQgle, though complex, horny structure placed at the margin 

 of the caudal sucker in the central line, but in some of the Gyro- 

 dactyli, the hooks are particularly numerous. As an intermediate 

 type, I may iastance Gyrodadylus elegans, where the caudal sucker 

 supports a pair of large laterally-recurved hooks, which are placed 



Fia. 14. — GrYEODACTTliTTS ELEGANS, Nordmann ; from the gills of Cyprinus hrama, showing an 

 almost completely developed embryo in the interior ; a, a — oesophageal bulb ; g — testis ; h, h 

 — posterior sucker ; i, i — the two large hoots ; k, le — the little marginal spines of the 

 sucker. Highly magnified. — Van Beneden. 



back to back in the centre of the disk, being connected at then- 

 upper or basal ends by the supervention of a transversely disposed 

 median, semilunar portion. A series of tentacles serve to in- 

 crease the prehensile action of the sucker. In many species 



