188 THE ZOOLOGIST. 



parasites were equally at home outside or inside, and simply 

 wandered in and out with ease and safety. 



This observation causes us to wonder whether it was the lack 

 of food-supply outside which caused the external parasites to 

 make their way inside the body cavity, where certainly the supply 

 of food juices would be richer. If this suggestion be correct, then 

 the Kerona must have at their disposal a " something " which 

 we have no ground for calling "intelligence," but still a "some- 

 thing " which enabled them to become aware that the ccelomic 

 cavity was richer in food material than the outside, and they 

 consequently made their way to the richer grounds. 



But if we, on the other hand, rule out this possibility and 

 claim it to be chemiotaxic stimulus, then we are in a quandary 

 as to why this stimulus did not come within the first few days 

 when the difference in strength between the juices inside and 

 outside was as great as it was when the apparent stimulus did 

 come. 



Another fact which this observation brings out is this, that 

 Kerona must not rigidly be classified as an ecto-parasite ; for 

 we have seen that for about fifteen days three of the parasites 

 were endo-parasitic in habit, and entirely immune from the 

 deleterious effects of the gastric ferments which dissolved and 

 killed other organisms stronger and larger than Kerona, for 

 example, Daphnia and small annulata. 



Besides, after the tenth day ecto-parasites became both ecto- 

 and endo- in habit. Therefore Kerona must not be classified as 

 rigidly confined to the species H. vulgaris and H.fusca, nor to 

 the endo-parasitic class alone, but also to the ecto-parasitic. 



Moreover, should Kerona be classified as a parasite in the true 

 sense ? It rather comes under the class of Commensals, where 

 some mutual benefit is derived. Can it be that the Kerona has 

 some part in cleansing the Hydra from foulness? Kerona 

 being almost always found on Hydra which inhabit stagnant 

 ponds. If the Kerona is to be reckoned as a parasite, why 

 should the Hydra not rid itself of the irritating depredator by 

 means of its powerful stinging nematocysts ? Instead, the Kerona 

 wanders inside and outside, over and around the trigger-hair or 

 cnidocil without causing the nematocyst to shoot out. Neither 

 do the amoeboid digestive cells inside envelop the internal ones 



