CLASSIFICATION OF LIVING THINGS. 



BOTH as a convenience in the study of organisms, and as 

 in some degree indicative of their genetic relationships, 

 various efforts have been made to arrange them under such a 

 systematic classification as would serve these ends. The work 

 involved in the foregoing laboratory course, while dealing 

 with a few typical organisms, and devoted chiefly to their 

 morphology and physiology, has also revealed unmistakable 

 relationships of structure and function, which in turn have 

 afforded evidence of the larger relationships of descent. 

 That a given kind or species of animals has descended from 

 a common line of ancestry is of course universally recognized. 

 That differing, but closely similar, species have likewise 

 descended from a common ancestor slightly more remote 

 is also generally recognized as a fact. Out of the study of 

 large series of such facts has come the conception of evolution, 

 long known to students of biology, but first brought into 

 prominence by Lamarck and Darwin. All modern sys- 

 tems of classification have been attempts to express the 

 facts of such relationships of descent or evolution. The 

 following partial and abbreviated tabulation of the animal 

 kingdom may illustrate, in a general way, the main features 

 of the subject. 



PHYLUM PROTOZOA. Unicellular, microscopic animals, 



or colonies of independent cells. 



Class 1. Rhizopoda. Protozoa possessing the power 

 of thrusting out pseudopodia. A shell is often 

 present. Amoeba, Arcella, Heliozoa. 



