600 SHEINA MARSHALL 



of Daphnia, is made to touch a tentacle tip, the capture 

 response immediately takes place. The food is thus brought 

 in to the hypostome ; and the tentacles, bending over, would 

 prevent escape were it alive. 



Chemical stimulation was also carried out with weak acetic 

 acid coloured with methylene blue. The strength used was 

 0-025 per cent., but this was probably much weaker by the 

 time it actually reached the Hydra. It did not injure the 

 tissues appreciably. 



Stimulation applied to Tentacle . — In about 60 per 

 cent, of the cases the tentacle contracted and the capture 

 response followed in about twenty seconds. In 30 per cent, 

 of the cases the whole Hydra swung away after forty 

 seconds, and in the remainder the animal contracted after 

 about thirty seconds. In one case a repetition of the stimulus 

 immediately after the response led to a second response 

 'without any pause. 



Body. — The body, when stimulated, either contracted or 

 swung away after thirty to forty seconds. In several cases 

 there was no result. 



Oral Cone. — When the oral cone was stimulated the 

 body contracted, sometimes immediately, sometimes after 

 thirty to forty seconds. 



Foot. — Stimulation of the foot resulted in a general con- 

 traction of the body, but it was very insensitive, and out 

 of eighteen stimulations twelve had no effect. In other cases 

 the body contracted after an interval varying from fifteen to 

 thirty seconds. 



From the above it will be seen that the head and foot regions 

 are much the most sensitive parts of the Hydra to mechanical 

 stimuli, while the foot appears to be comparatively insensible 

 to chemical stimuli, at least to acetic acid. 



Egg Formation. 



When the Hydra is about to form an egg the interstitial 

 cells are multiplied enormously and form a mass bulging 

 out the ectoderm. Characteristic changes take place in their 



