ILLUSTRATIONS 



FIG. PAGE 



1. Diagram of the Primary Sensory and Motor Neurones of the Spinal 



Cord of a Vertebrate 17 



2. Diagram of the Primary Sensory and Motor Neurones of the Ventral 



Ganglionic Chain of the Earthworm 18 



3. Ectodermic Layer from the Tentacle of a Sea-anemone 20 



4. Diagram of the Canal System of a Calcareous Sponge 26 



5. Radial Portion of a Transverse Section of Stylotella 30 



6. Diagram of a Finger of Stylotella 32 



7. Dermal Membrane Over a Subdermal Cavity in the Sponge Stylotella. 34 



8. Three Dermal Pores in Stylotella 35 



9. Fingers of Stylotella in a Strong Current of Seawater 40 



10. A Finger of Stylotella Protected from a Gentle Current of Seawater . . 41 



11. Diagram of the Apparatus for Measuring the Strength of a Current of 



Seawater Produced by Stylotella 44 



12. Diagram of the Apparatus to Test the Strength of the Dermal Pores 



of Stylotella 47 



13. Diagram of the Heart of a Fish 54 



14. Diagrammatic View of a Longitudinal Section of Scalpa; Enlarged 



View of an Isolated Heart of Scalpa 57 



15. Side View of the Ctenophore Mnemiopsis leidyi 67 



16. Plan of a Temperature Box 69 



17. Diagram of a Longitudinal Section of the Sea-anemone Metridium. . . 77 



18. Transverse Section of the Sea-anemone Metridium 78 



19. Diagram of the Ectoderm of a Sea-anemone 80 



20. Diagram of a Partial Longitudinal Section of the Sea-anemone 



Metridium 85 



21. Metridium With Its Column Completely Girdled by a Cut that Passes 



at all Points Entirely Through the Wall 91 



22. Metridium in Whose Column Wall an Oblong Incision Has Been 



Made so that the Resulting Piece is Attached to the Animal 

 Only by the Mesenteries 92 



23. Metridium Cut Vertically in Two Except in the Region of the Lips . . 92 



24. Metridium from Which an Equatorial Tongue Has Been Cut from the 



Column 93 



25. Metridium from Which a Tongue Running from the Pedal Disc to the 



Equator of the Column Has Been Cut 94 



26. Metridium from Which a Portion of the Pedal Edge of the Column 



Has Been Partly Cut Off 94 



11 



