- Introduction
- Segmentation
- Ideal Serial Homology
- Parabiosis
- Vertebrate and Arthropod Progenitors; Their Form and Origin
- The Vertebrate Skull
- The Axial Skeleton
- The Appendicular Skeleton
- Ontogeny and Phylogeny
- Verification
- Irreversibility
- Incipience and Preadaptation
- Specialization
- Stripes
- Vestigial Segmentation in the Skin
- The Fossil Record
- Traditional Ideas about Vertebrate Progenitors
- Conclusion
- Literature cited
- Glossary
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