52 DOCTRINE OF EVOLUTION 



activity, for fingerlike processes called pseudopodia 

 are pushed out tentatively in many directions to be 

 followed as circumstances direct by the materials of 

 the whole cell body. Other protozoa differ in possessing 

 constant forms, or in having constant vibratile pro- 

 cesses, or shells of some kind, while in still other cases 

 like individuals combine to make colonies which are 

 more or less definite and permanent. Here at the very 

 foot of the organic scale are found animals which seem 

 to be entirely different from those above. Upon 

 examination they, like Hydra, prove to be the same as 

 regards the number and kind of functions they perform, 

 but in structural regards their evolutionary relation 

 to all higher animals is indicated solely by the fact 

 that they are cells composed of protoplasm. Never- 

 theless the principle which states that resemblance 

 means consanguinity still holds true, for cellular con- 

 stitution is a unique possession of things of the living 

 world, — something which demonstrates the common 

 origin of all living things just as truly as the '^cat-ness'' 

 of our first series of examples reveals for a smaller 

 group the significance of likeness and the nature of 

 the basic law of comparative anatomy. 



Employing a figure of speech, we have climbed down 

 the animal tree from the higher regions where the 

 mammals belong. Having reached the very foot of 

 the trunk we are in a position to review and summarize 

 the evidences which we have discovered all about us 

 as we have descended. The various examples we 

 have mentioned and the groups to which they belong 



