AMCEB^. 141 



The inference from the one-celled germ-form to the 

 one-celled parent-form is so simple, and yet so full of sig- 

 nificance, that it is impossible to lay too much stress upon 

 it. Naturally the first question arising is, whether there 

 exist at the present day any one-celled organisms, from the 

 form of which we may draw an approximately correct 

 conclusion as to the one-celled ancestors of many-celled 

 organisms ? The answer to this question is undoubtedly 

 affirmative. There are most certainly one-celled organ- 

 isms now in existence, the whole organization of which is 

 but that of a permanent egg-cell; there are independent 

 one-celled organisms, which never undergo any further 

 development, which pass their whole lives as simple cells, 

 and as such reproduce themselves without attaining to any 

 higher development. We now know a great number of such 

 one-celled organisms, — for example, the Gregarina, Flagellata, 

 Acineta, Infusoria, etc. But one among them is especially 

 interesting to us, because it afibrds the most complete 

 answer to our question, and must be regarded as the one- 

 celled primary organism which most nearly approaches the 

 type-form of the race. This organism is the Amoeba. 



The name AmcebfB has long been applied to a number of 

 microscopic one-celled organisms, which are by no means 

 rare, and are indeed widely distributed, principally in fresh 

 water, but also in the ocean ; lately they have been found 

 inhabiting moist earth. When one of these living Amcebge 

 is placed in a drop of water under the microscope and 

 greatly magnified, it appears to be a roundish body of very 

 irregular and varying form (Fig. 13). Enclosed in the soft, 

 slimy, half-fluid body, which consists of protoplasm, we can 

 only see a small solid or vesicular substance, which is the 



