LIST OF'ILLUSTEATIONS. 



1-8. Antceba . 2 



9. Farameciimi aiirelia . . .... .4 



10. Vorticella ....... . . 9 



11. Hydra : Diagrammatic longitudinal section ... .15 



12. „ Section of the body-wall, highly magnified . 17 



13. Fasciola liepatica : Diagrammatic figure of the digestive, ex- 



cretory, and nervous systems 29 



14. „ The repi'oductive system . . '. 31 

 15-19. „ A series of stages in the life-history 34 



Fig. 15. The free-swimming embryo 

 „ 16. A sporocyst, containing rediie 

 „ 17. A young redia 

 „ 18. An adult redia, containing a daughter- 



redia and cercarias 

 ,, 19. A free cercaria 



20. Hirudo medicinalis : The ventral surface . . , 43 



21. „ Diagrammatic figure of the vascular, renal, re- 



productive, and nervous systems . . . . 43 



22. „ Diagrammatic transverse section through the 



middle of the body 54 - 



23. Lumbricus herculeus : Longitudinal vertical section through 



the anterior part of the animal . . . . 64 



24. ,, Plan of the reproductive organs .... 71 



25. „ Diagrammatic transverse section through the 



middle of the body 77 



26. Anodonta cygnea : Dissectioli from the right side, to show the 



heart and gills 90 



27. „ Dissection from the right side, to show the diges- 



tive and renal systems 96 



28. „ Diagrammatic transverse section through the 



middle of the ventricle 106 



29. HeUx pomatia : Dissection from the right side, to show the 



mantle-cavity ....... 115 



80. „ Dissection from the right side, to show the diges 



tive and reproductive systems .... 120 



31. „ Section along the axis of the shell, transverse to 



the foot 130 



32. Astacus fluviatilis : Transverse section through the abdomen . 134 



33. „ The oral appendages 140 



34. „ Diagrammatic transverse section through the 



thorax 144 



35. „ Dissection of a male from the right side , . 148 



