GASTRULA | O | III | III Stages 6-11: | { with two | _Hydra, Olynthus_,| | | INVERTEBRATE | { germinal layers | _Orthonectida_ | | | METAZOA- | { 7. PLATODES I. | 7. CRYPTOCŒLA | O | ? | I ANCESTORS | { _Platodaria_ | (_Convoluta_) | | | 6-8: | { (without nephridia)| (_Proporus_) | | | Cœlenteria, | { 8. PLATODES II. | 8. RHABDOCŒLA | O | ? | I without anus | { _Platodinia_ | (_Vortex_) | | | anus or | { (with nephridia) | (_Monotus_) | | | body-cavity | | | | | | | | | | | { 9. PROVERMALIA | 9. GASTROTRICHA | O | ? | I | { _Rotatoria_ | _Trochozoa_ | | | | { Primitive worms | _Trochophora_ | | | 9-11: | {10. FRONTONIA | 10. ENTEROPNEUSTA | O | ? | I Vermalia, | {(_Rhynchelminthes_)| _Balanoglossus_ | | | with anus and| { Snouted worms | _Cephalodiscus_ | | | body-cavity | {11. PROCHORDONIA | 11. COPELATA | O | II | II | Worms with chorda | _Appendicaria_ | | | ------------+---------------------+-------------------+-----+-----+----- | {12. ACRANIA I. | 12. LARVÆ OF | O | III | II | { (Prospondylia) | AMPHIOXUS | | | Stages 12-15:| {13. ACRANIA II. | 13. LEPTOCARDIA | O | I | III MONORRHINA- | { Later skull-less | Amphioxus | | | ANCESTORS | { animals | (Lancelet) | | | Earliest | {14. CYCLOSTOMA I. | 14. LARVÆ OF | O | III | II vertebrates, | { (Archicrania) | PETROMYZON | | | without jaws| {15. CYCLOSTOMA II. | 15. MARSIPOBRAN- | O | I | III or pairs of | { Later round- | CHIA | | | limbs, with | { mouthed animals | Myxinoides | | | single | { | Petromyzontes | | | nostril | | | | | -------------+---------------------+-------------------+-----+-----+----- 2B.--MAN'S GENEALOGICAL TREE--_Second Half_ LATER ANCESTRAL SERIES, WITH FOSSIL REMAINS, BEGINNING IN THE SILURIAN