LIST OF FIGURES 



Fig. I . Diagram of nuclear division. 



2. Two idants of Ascaris megalocephala. 



3. Diagram of the cell-generations in the fore-limb of a newt. 



4. Multiplication by fission in a marine worm {Myrianida). 



5. Transverse section through the 'zone of gemmation' in a 



fresh-water worm (i\'«;.f). 



6. An earlv stage in the formation of a bud in a Hydroid polype 



{Eudendriu/ti). 



7. Apex of a shoot of a fresh-water Alga {Ckara). 



8. Female water-flea {Dapknia), with summer eggs. 



9. Nauplius larva of Leptodora kyalina. 



10. Alternation of generations in Bougainvillea. 



11. Strobilation of a Medusa. 



12. Degeneration of a Medusa into a mere gonophore. 



13. Early stages of development of the primitive germ-cells in 



Sagitta. 



14. Early stages in the development of the primitive germ-cells in 



Moifia. 



15. Early stage of the embryo of Rhabditis nigrovcnosa. 



16. Diagram of the germ-track in Rhabditis nigrovenosa. 



1 7. Volvox and Pandornia. 



18. Process of fertilisation in Ascaris megalocephala . 



19. Diagram to illustrate the composition of the idants out of 



individually different ids. 



20. Formation of spermatozoa in Ascaris megalocephala. 

 \ 21. Formation of ova in Ascaris megalocephala. 



\ 22. Diagram to illustrate the combination of idants in hybrids. 



23. The two varieties of Cypris reptans. 



24. Bonellia viridis, male and female. 



xxiii 



