III. THE STRUCTURAL UNITS OF LIVING 

 MATTER. 



The analyses of the chemist tell merely what elements 

 or combinations of elements enter into the building of 

 living matter. The principal interest in such analyses 

 lies in the proof they give that all living matter, plant or 

 animal, consists of essentially the same chemical elements. 



When we speak of the struc- 

 tural composition of a given 

 plant or animal we do not refer 

 to its chemical make up, but to 

 the form which these compounds 

 take. Thus the most evident 

 structural forms these com- 

 pounds take in our bodies we 

 call eyes, ears, bones, flesh, etc., 

 while in plants they receive the 

 name of leaves, roots, stems, etc. 

 Gross structure of the body. 

 — Roughly, the body consists 

 of a head, a trunk, and append- 

 ages (arms and legs). All these 

 parts agree in being made up 

 hopper split to show the external of soft matter Supported by a 



skeleton. Hard parts are in j. i /• i i 



black. framework oi hard matter. 



Lower animals, like the crayfish 



and grasshopper, also consist of hard and soft matter, but 



with them the hard matter, when present, is on the 



28 



Fig. 6 — A, diagram of a human 

 trunk split to show the internal 

 skeleton. 71, diagram of a grass- 



