12 EXPLANATION OF THE FIGURES. 



THE CHART OF ZOOLOGICAL REGIONS, page 195, is intended to show 

 the limits of the several Faunas of the American Continent, correspond- 

 ing to the climatal regions. And as the higher regions of the mountains 

 correspond in temperature to the climate of higher latitudes, it will be 

 seen that the northern temperate fauna extends, along the mountains of 

 Mexico and Central America, much farther towards the Equator than it 

 does on the lower levels. In the same manner, the southern warm fauna 

 extends northward, along the Andes. 



FIG. 



1. Simple cell, magnified, as seen in the house-leek. 



2. Cells when altered by pressure upon each other ; from the pith of elder. 



3. Nucleated cells, (a,) magnified; b, nucleolated cells. 



4. Cartilaginous tissue from a horse, magnified 120 diameters. 



5. Osseous tissue from a horse, magnified 450 diameters. 



6. Nervous fibres, showing the loops as they terminate in the skin of a 



frog. 



7. Gray substance of the brain, magnified. 



8. Head of an embryo fish, to show its cellular structure throughout. 



9. Diagram, to show the nervous system of the Vertebrates, as found 



in a monkey. 



10. Diagram of the nervous system of the Articulates, as seen in a lobster. 



11. Diagram of the nervous system of the Mollusks, as found in Natica 



heros. 



12. Diagram of the nervous system of the Radiates, as found in Scutella, 



( Echinarachnius parma. ) 



13. Section of the eye. a, optic nerve ; b, sclerotic coat ; c, choroid coat; 



d, retina ; e, crystalline lens ; f t cornea ; g, iris ; h, vitreous body ; 

 i, chamber, divided by the iris. 



14. Diagram, showing the effect of the eye on rays of light. 



15. Position of the eye of the snail. 



16. Eyes (ocelli) of the spider. 



17. Eye-spots of a star-fish, (Echinaster sanguinolentus.) 



18. Compound eyes, showing the arrangement of the faoettes, and their 



connection with the optic nerve, as seen in a crab's eye. 



19. Diagram of the human ear, to show the different chambers, canals, 



and bones. 



20. Tympanum and small bones of the ear, twice the natural size ; c t 



tympanum ; m, malleus ; n, incus ; o, orbiculare : s, stapes. 



21. Section of the brain of a crow, showing the origin of the nerves of 



the special senses. 



22. Diagram of the larynx, in man. 



23. Larynx of the merganser, (Mergus merganser.) 



24. Nests of Ploceus Philippinus, male and female. 



25. Distribution of nerves to the muscular fibres* 



26. Test, or crust-like covering of an Echinoderm, (Cidaris.) 



