2 1'HYSIOLOGY AND MORPHOLOGY OF ANIMALS. 



f Areolar. 



t, Connective } Fibrous. 



( Dermoid. 



( Permanent. 



±. Cartilage \ ™ 



5 ( Temporary. 



! Bone proper. 



3. Bone ] Dentine. 



' Enamel. 



( Striated. 



4. Muscle \ ,., . . . . 



^ ( Nonstnated. 



( Gray granular. 



5 ' " ) White fibrous. 



6. Epithelium 



Rounded. 

 Tesselated. 

 Columnar. 

 I Ciliated. 



Thus, then, there are composing the animal body six 

 different kinds of tissues with their varieties, each with 

 a different function, and all co-operating to produce one 

 end, viz., the conservation of the life and happiness of 

 the organism. This is the type and expression of or- 

 ganization, but it is realized only in the higher animals. 

 As we go down the scale either in the animal series or in 

 the embryonic series, one tissue after another disap- 

 pears, first bone, then cartilage, then muscle, then nerve, 

 until only unmodified cell aggregate remains, and still 

 lower only a single unmodified cell remains. The cor- 

 responding functions merge into one another, and at 

 the same time become less and less perfect, until every 

 part performs, but very imperfectly, all the functions of 

 life. Or, taking the reverse order, which is the order of 

 evolution : first there is only one cell performing all the 

 necessary functions of life, but very imperfectly; next 

 an aggregate of unmodified and therefore similar cells 



