ECTOPARASITIC PROTOZOA 21 



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they are on the fish, since they withstand treatment practically 

 as well as their hosts. Epidemics may be promptly checked, how- 

 ever, by a rapid circulation of fresh water in the infected ponds. 

 Barthelemy (1926) advises that the pond be drained and exposed 

 to sun and heat. Also the hands of workmen and the tools used 

 should be disinfected with milk of lime or one per Cent formalin. 



Description: Size, adult forms soOfi-iooo/x, young forms 40/1-50//; young 

 specimens penetrate the epithelium of soft-skinned fish and develop to 

 maturity in epithelial pockets, then they burst out of the pustules and drop 

 to the bottom of the ponds where they encyst and give rise by repeated 

 divisions to about 256 small ciliates which represent the infective stage; 

 alternates between free-living and parasitic existence. 



(e) Prorodon teres Ehrenberg, 1883. 



Ordinarily representatives of this species are free-living ciliates 

 which feed on small animals and plants; but Reukauf (1912) re- 

 cords a very interesting observation in which they were found 

 freely invading the enteric cavity of Hydra. He also reports that 

 on some occasions this large gymnostomatous ciliate would enor- 

 mously distend its cytostome and slip itself over the end of a 

 tentacle, remaining there until it had digested off the end. 



Description: Size 200/i x 300/1; ordinarily a free-living ciliate, but may 

 become temporarily parasitic on Hydra. 



Order hypotricha. 



Kerona pedicidus (O.F.M.) Ehrbg. 



O. F. Miiller was the first to give this so-called "polyp louse" a 

 scientific name. In 1786 he gave a rather meager description of it 

 under the name Cyclidimn pedicidus. Ehrenberg (1838) gave a 

 very accurate description of this form, but called it Kerona polyp- 

 orum. This has led to considerable confusion, some authors call- 

 ing this ciliate K. pedicidus, and others calling it K. polyporuni. 

 Apparently the latter name is a synonym for the former. 



This protozoon creeps over the surface of various species of 

 Hydra, feeding upon free-living protozoa and also upon the dead 

 epithelial cells of its host. Possibly it feeds on the living cells of 

 its host under certain conditions. Schulze (1913) observed that 

 Hydra heavily infected with K. pedicidus possessed knobbed or 

 hypertrophied tentacles. He attributed this pathological condition 

 to the presence of the protozoa. As this condition in Hydra may 

 be induced by various other factors, Schulze's interpretation is 



