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SCIENCE PROGRESS. 



ceased with the withdrawal of oxygen. The protoplasmic 

 movements were arrested and the Rhizopod remained 

 motionless until a fresh supply of oxygen caused the 

 pseudopodia once more to expand. The formation of 

 pseudopodia, and consequently the change of shape of the 

 body, is thus evidently in the highest degree dependent on 

 the supply of oxygen. On the other hand, total retraction of 

 the pseudopodia can be caused by the introduction of certain 

 acids, alkalies, or salts, into the medium surrounding the body. 

 Sulphuric acid, potassium hydrate, or potassium sulphate, of 

 a certain degree of concentration, added to the water con- 

 tainingan Amoeba at once cause retraction of thepseudopodia. 

 The dependence of the form of the organism upon its 

 chemical relations with the surrounding medium is also clearly 

 shown by the following facts, which a series of experiments 

 have recently enabled me to demonstrate. Amoebse, as 

 is well known, are usually divided into different species 



Different Forms of the Same Species of Amoeba. 

 a. — Spherical, during strong excitation. 

 b. — Beginning to move in the form o{ Amoeba proteus. 

 c. — Usual form of Amoeba Umax. 

 d. — Beginning to assume the form of Amoeba radiosa after addition to the water 



of Potassium hydrate. 

 e,f. — Form of Amoeba radiosa under the influence of potassium hydrate. 



according to the form of their pseudopodia. The Amoeba 

 proteus is distinguished by broad finger-shaped pseudo- 



