PROTOZOA TO WORMS 37 



Professor Huxley has said, "whirlpools on the sur- 

 face of Nature ; " when the whirl of exchange of particles 

 ceases we die. We have seen that the fusion of two 

 amcebse results in a new rejuvenated iadividual. Why 

 is a mixture of two protoplasms better than one ? We 

 can frame hypotheses; we know nothing about it. 

 What of the mind of the amoeba ? A host of questions 

 throng upon us and we can answer no one of them. 

 All the great questions concerning life confront us here 

 in the lowest term of the animal series, and appear as 

 insoluble as in the highest. 



Our second ancestral form is also a fresh- water ani- 

 mal, the hydra. This is a little, vase-shaped animal, 

 which usually lives attached to grass-stems or sticks, 

 but has the power to free itself and hang on the surface 

 of the water or to slowly creep on the bottom. The 

 mouth is at the top of the vase, and the simple, undi- 

 vided cavity within the vase is the digestive cavity. 

 Around the mouth is a ring of from four to ten hoUow 

 tentacles, whose cavities communicate freely under- 

 neath with the digestive cavity. Not only is food 

 taken in at the mouth, but indigestible material is 

 thrown out here. The animal may thus be compared 

 to a nearly cylindrical sack with a circle of tubes at- 

 tached to it above. The body consists of two layers 

 of cells, the ectoderm on the outside and the entoderm 

 lining the digestive cavity. Between these two is a 

 stmctureless, elastic membrane, which tends to keep 

 the body moderately expanded. 



The food is captured by the tentacles ; but digestion 

 takes place only partially in the digestive cavity, for 

 each surrounding cell engulfs small particles of food 

 and digests them within itself. The entodermal cells 



