A NOTE ON PARASITIC KEBONA. 187 



find that it had fifteen tentacles instead of the usual number 

 possessed by this species, namely, six to ten tentacles. Interest 

 was further aroused by the movements on the surface of the 

 ccelenterate of eleven protozoal parasites. "When the high power 

 was brought to bear upon the organisms, it was found that eight 

 were wandering over the outside of the Hydra, while three were 

 quite at ease inside the body cavity — apparently wandering 

 aimlessly over the endodermic cells. 



The parasites were all of the same species, and were 

 identified as Kerona polyporum : — 



Description. — Miill., Ehr. Genus of infusoria of the family 

 Oxytrichina. 



Characters. — Body covered over with cilia, hooks present, but 

 no styles. Body flat or depressed, whitish, elliptico-reniform 

 with a row of longer cilia in front of the mouth ; length approxi- 

 mately 1-144". 



These eleven parasites were found on and in Hydra viridis, 

 while it is stated by many that the host is confined to the 

 species H. fusca and H. vulgaris. Thus we see that the limit 

 is too narrow, and that the range stretches over and includes 

 Hydra viridis as an occasional host of Kerona. 



It has also been generally understood that Kerona is an 

 ecto-parasite, found only on the outside of Hydra, yet here 

 three were in the body cavity. For ten days the Hydra and 

 parasites were kept under observation. The ratio during that 

 time still remained the same, eight remaining on the outside 

 and three occupying the ccelomic cavity, all exhibiting the 

 usual apathetic attitude of parasites in general ; namely, they 

 were entirely indifferent to movements of the host, wandered at 

 leisure over the surface, living probably by osmotically absorb- 

 ing the nutriment found in connection with the host. The 

 water in which they were kept during these ten days was well 

 supplied with Entomostraca and other food-supply for the 

 Hydra. 



One of the Kerona divided on the fourth day. Thus the ratio 

 was nine outside and three inside. After the tenth day no food 

 was supplied, and to one's astonishment on the twelfth day 

 many of the external parasites were found to have made their 

 way into the ccelomic cavity ; and from this time on, the 



