DIFFERENTIATION OF THE ANIMAL BODY. 123 



B. Active tissues. 



III. Muscular (fibrous, little intercellular substance). 

 Kinds: plain, cross-striate fibres. 



Functions: sensitiveness to nervous stimuli, contraction, 

 motion. 



IV. Nervous (branched and elongated). 



Form: central cell (ganglion) with fibrous branches 



(axon, dendrori). 



Functions: reception of general stimuli, transmission of 



impulses, interpretation of these impulses, and starting 



responses. 



4. Epithelial tissues arise from ectoderm, entoderm, and mesoderm ; 

 connective tissue from mesoderm; muscular tissue chiefly from 

 mesoderm; nervous tissue from ectoderm. 



134. Supplementary Exercises for Themes. i. Differences be- 

 tween plant tissues and animal tissues. 



2. The finer structure of the cross-striate muscular fibres. 



3. How are nerves united with muscles? 



4. Why would you expect nervous elements to arise from ecto- 

 derm? Why would you expect the nerve centres to sink below the 

 surface into the deeper parts of the body ? 



5. Why are the epithelial cells the glandular cells? 



6. What advantage is there in the fact that the epithelial cells 

 retain considerable power of division? 



7. What is there suggestive about the fact that it is epithelium 

 which produces ova and sperm? 



135. Technical Term to be Defined. Mesoderm, coelom, epithe- 

 lium, connective tissue, intercellular substance, mucous membrane, 

 serous membrane, tendon, ligament, dentine, enamel, ganglion, 

 axon, dendron. 



