LIST OF ILLUSTRATIONS 



1. Digestive, nervous, generative, and excretory systems of 



the Liver-fluke ...... 4 



2. Stages in the life-history of Distomum hepaticum . 1 1 



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 



11. 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 



I5 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 



