LIST OF ILLUSTRATIONS. 



FIGUBE PAGE 



1-8. Amoeba 2 



9. Paramecium aurelia ....... 4 



10. VorticeUce. . 9 



11. Monocystis ......... 14 



12. Hydra : Diagrammatic longitudinal section ... 19 



13. Section of the body-wall, highly magnified . . 21 



14. Obelia . 31 



15. Fasciola hepatica : Diagrammatic figure of the digestive, ex- 



cretory, and nervous systems .... 36 



16. The reproductive system . . . . .38 

 17-21. A series of stages in the life-history ... 42 



Fig. 17. The free-swimming larva 

 18. A sporocyst, containing redise 

 19. A young redia 

 20. An adult redia 

 21. A free cercaria 

 21a. Tapeworm 47 



22. Hirudo medicinalis : The ventral surface .... 53 



23. Diagrammatic figure of the vascular, renal, re- 



productive, and nervous systems . . 53 



24. Diagrammatic transverse section through the 



middle of the body 64 



25. Lumbricus terrcstris : Longitudinal vertical section through 



the anterior part of the animal ... 71 



26. Plan of the reproductive organs ... 78 



27. Diagrammatio transverse section through the 



middle of the body ..... 85 



28. Anodonta cygnea : Dissection from the right side, to show the 



heart and gills 98 



29. Dissection from the right side, to show the 



digestive and renal systems . . . 104 



30. Diagrammatio transverse section through the 



middle of the ventricle . . . .114 



31. Helix pomatiai) Dissection from the right side, to show the 



mantle-cavity ...... 124 



32. Dissection from the right side, to show the 



digestive and reproductive systems . . 128 



33. Section along the axis of the shell . . 138 



34. Astacus pallipes : Transverse section through the abdomen . 142 



35. The oral appendages 148 



36. Diagrammatic transverse section through the 



thorax 152 



