LIST OF ILLUSTRATIONS 



Fig. I. Digestive, nervous, generative, and excretory systems of 



the Liver-fluke ...... 4 



,, 2. Stages in the life-history of Distomum hepaticum . n 



,, 3. Lumbricus herculeus ..... 18 



,, 4. Dissections showing the organs contained in the first 



sixteen somites of Lumbricus herculeus . . 22 

 ,, 5. Diagrams showing the structure of the nephridium of the 



Earthworm . . . . . .25 



,, 6. Diagrams illustrating the arrangement of the blood- 

 vessels in Lumbricus herculeus .... 29 



,, 7- A tranverse section through the intestinal region of 



Lumbricus herculeus . . . . .31 



,, 8. Segmentation and early stages of development of Lum- 

 bricus ....... 37 



,, 9. Later stages of the development of Lumbricus . . 41 

 ,, 10. Drawings of larval stages and adult of Polygordius and 



of the anterior end of Nereis rubicunda . . 47 



,, 1 1. A view of Anodonta cygnea after removal of the left valve 56 



,, 12. Diagrams of the anatomy of Anodonta cygnea . . 58 

 ,, 13. Diagrammatic transverse sections through Anodonta 



cygnea ....... 60 



,, 14. Diagrams of a gill filament of Mytilus edulis and of a 



vertical section through Anodonta cygnea . . 62 



,, 15. Glochidium larva of Anodonta .... 66 



,, 1 6. Helix aspersa, the shell and entire animal removed from 



the shell . . . . . .71 



,, 17. Dissection of Helix aspersa 75 

 ,, 1 8. Nervous systems of Helix aspersa, Limnsea, and Paludina 



vivipara. ...... 78 



,, 19. Eye and Radular teeth of Helix .... 80 



,, 20. Diagrams illustrating the development of a Gastropod . 85 



,, 21. Side view of Apus cancriformis .... 93 



, , 22. Appendages of Apus cancriformis ... 97 



