CAUSE OF EVOLUTION 401 



the blood of the snail arid in 1859 I showed that these 

 colorless blood corpuscles like independent amoeba can 

 assimilate solid particles, can, therefore, eat. Lately it 

 has been found that very many different cells, if they 

 have room, are able to move and eat and to act entirely 

 like amoeba. 



The capacity of the naked cell to make these character- 

 istic amoeboid movements depends on the contractility 

 (or automatic movableness) of the protoplasm. This 

 seems to be the universal property of all young cells. 

 Where they are not surrounded by a strong membrane 

 or shut up in a cell prison, they are all capable of amoe- 

 boid movements. This is as true of the uncovered egg 

 cell as of other uncovered cells of the moving cells of 

 various kinds, lymph cells, mucous cells, etc. 



"Our examination of the egg cell and comparison of it 

 with the amoeba has afforded us the best and surest 

 basis for the history of the germ as well as for the history 

 of the tribe. From it we have drawn the conclusions that 

 the human egg is a simple cell ; that this egg cell is not 

 essentially different from those of other mammals and 

 that we must therefore infer the existence of a primeval 

 one-celled ancestral form, which in all essential points 

 was of amoeboid form. 



"The very important bearing which the Cell Theory 

 has on the whole conception of organic nature is thus 

 very clearly seen. The 'Place of man in nature' is radi- 

 cally explained by it. Without this theory, man is an 

 unintelligible puzzle. Philosophers, therefore, and cer- 

 tainly the psychologists, ought especially to acquaint 

 themselves thoroughly with the Cell Theory. The human 

 mind can only be really understood by means of this 

 theory and its simplest form is illustrated in the amoeba. 

 The extant amoeba and the kindred one-celled organism, 



