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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I3I 



deliberately presents itself to the head end of a fish has perhaps not 

 been observed, but the fish unwittingly engulfs the copepod as food, 

 which is of course just what the prospective parasite wanted it to do. 

 To save itself from being swallowed the copepod grasps a gill arch of 

 the fish with the hooks of its maxillipeds. Then it pushes its head into 



Fig. II. — Copepoda : Lernaeopodidae. Developmental stages of fish parasites 

 (from Wilson, 1910, 1915). 

 A, Achtheres ambloplitis Kellicott, first copepodid, with filament (/) in head. 

 B, same, second copepodid. C, same, with filament extruded and attached. D, 

 same, adult male. E, same, adult female. F, Salminicola siscowat (Kellicott), 

 egg-carrying female. 



the soft skin of a gill, which act breaks the cuticle over its head and 

 releases the filament. The filament protrudes into the wound of the 

 gill and the end spreads out into a disc that anchors the parasite inside 

 the gill chamber of the fish. 



The first copepodid larva of Achtheres (fig. ii A) undergoes a 

 moult and enters a second copepodid instar (B), which is decreased 

 in size and has taken on a different shape. The swimming legs, being 

 now useless organs, are greatly reduced and later disappear (C). 

 The mandibles have become toothed piercing organs for feeding. The 



