CELLULAR DIFFERENTIATION. 57 



character : abundant intercellular substance, 

 form : vesicular, gelatinous, fibrous, cartilagi- 

 nous, osseous-, etc. (blood and lymph). 

 B. The active tissues. 



III. Muscular : 



function : irritability, especially to nervous 

 stimuli ; contraction in a definite direction. 



form: plain and cross-striate (depending on 

 the differentiation of the contractile sub- 

 stance). 



IV. Nervous : 



function : reception of general stimuli, 



transmission of impulses, interpretation, 



arid the initiation of appropriate responses. 



form: central cells (ganglion) with fibrous 



branches (axon, dendron). 



6. The epithelial tissues arise from ectoderm, entoderm and 

 mesoderm ; the connective tissue, from mesoderm ; the muscu- 

 lar, chiefly from mesoderm; and the nervous tissue, from 

 ectoderm. 



84. Exercises for the Laboratory (these may be made as 

 extensive as time and facilities will allow). 



i. Temporary demonstrations of the simpler tissues should 

 be made by the teacher or pupil, by teasing out with needles 

 small portions of the appropriate material in a drop of water 

 on the slide. 



(a) Blood. Compare that of earth-worm or insect, frog, 

 man. Place a drop of fresh blood on the slide and cover. 

 Examine at once. The teacher should have a permanent 

 preparation of the blood of the frog, stained to show nucleus 

 of corpuscles. 



(b) Epithelium. Mesentery of cat; film shed from skin 

 of frog kept a few days in captivity; cells scraped from the 

 oesophagus of a recently killed frog. 



(c) Connective Tissue. Found surrounding muscle, i. e., 

 lean meat. Compare tendon. 



