ILLUSTRATIONS 



FIG. PAGE 



1. Oscillograph tracing of "action potential" 



running along a nerve fibre 132 



2. The jelly-fish ^wr^/m 133 



3. A human eye cut in half to show the internal 



structure 138 



4. The eye of a bird cut in half to show the internal 



structure 148 



5. The cephalothorax in three different sorts of 



spiders to show the ocelli 161 



6. Front view of head of Privet Hawk Moth 



caterpillar, showing ocelli 163 



7. Front view of a Honey Bee's head, showing 



ocelli and compound eyes 163 



8. A section of the compound eye of a Honey Bee 164 



9. A single ommatidium from the eye of a Honey 



Bee 165 



10. A diagram of the human ear 170 



11. A cross-section of one turn of the spiral cochlea 1 72 



12. A Lung-fish, showing the lateral line 181 



13. The head of a Fulmar Petrel, showing the 



tubular nostrils 199 



14. Section of part of the tongue, showing taste 



bulbs 203 



15. A single taste bulb, showing ends of the receptor 



cells 203 



16. A Catfish, showing the barbels 210 



17. The head end of a marine worm, showing the 



four "feelers" beside the four eyes 212 



18. A diagram of the three semi-circular canals, 



showing their connection with the cochlea 219 



19. (a) Freshwater crayfish, showing the second 



pair of feelers 222 



