GYRODACTYLID.E. 



45 



of peculiar liooks projecting from the posteriorly- situated sucking 

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

 to a single, 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 instance Gyrodadylus elegans, where the caudal sucker 

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



n-/ 



Fio. 14. — GrYEODACTYiitrs ELEGANS, Nordmann ; from the gills of Cyprinus brama, showing an 

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

 — posterior sucker ; i, i — the two large hooks ; /c, h — the little marginal spines of the 

 sucker. Highly magnified. — Yan Beneden. 



back to back in the centre of the disk, being connected at their 

 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 



