296 D. D. WHITNEY. 



The loss of the algae does not seem to interfere with the proc- 

 ess of bud formation in the slightest degree. Experiments VIII. 

 and X. show that if the white hydras are fed sufficiently they will 

 produce buds at a normal rate and in a normal manner. 



It is a well-known fact that green hydras will live several weeks 

 without food but of many hydras that I have kept 2-5 weeks in 

 various experiments without food none ever produced buds, 

 thus showing that the alga does not furnish food enough for 

 bud formation. However, if sufficient food is given to either the 

 white or green hydras buds soon appear. 



The hydras from which all algae have been extracted do not be- 

 come reinfected with the algae. In Experiment X. both lots of 

 the white hydras were kept in large balanced aquaria in which 

 there were hundreds of green hydras, but they remained white. 

 Furthermore the white hydras were fed upon rotifers, the diges- 

 tive tract of which was usually filled with Euglena viridis. It 

 will be recalled that Sallitt believed that the green bodies of Eu- 

 glena were identical with those of the green hydra. However, the 

 colorless hydras are not infected by even this contaminated food 

 supply. 



The reappearance of the algae in some of the supposed white 

 hydras can be readily explained by the supposition that all of the 

 algae were not removed from the endoderm cells of the hydras be- 

 fore they were transferred to spring water. When the animals 

 were placed again in their normal environments the alga began 

 to grow and reproduce itself until the hydras became as green as 

 normal ones. 



The white hydras seems to respond to the stimulus of light in 

 the same manner as the green hydras. In Experiment XIII., 

 where the hydras were starved, some of them collected on the 

 lighted side of the dish and the others remained upon the bottom. 

 None were found on the least illuminated side of the dish. 



In Experiment X., lot A, the white hydras were suspended in 

 the large aquarium in a small dish. They did not leave the 

 dish, but climbed upon its lighted side. The food, Hydatina 

 senta, shows no reaction to light, so that it cannot be supposed 

 that the hydras moved towards a food supply. 



Some of the white hydras of lot B in the same experiment left the 



