Mammalia. Sauropsida. | | |____________________________| | Proto-Amniota. Amphibia. | | |_____________________| | Proto-Pentadactyloidei. | Teleostei. | | | Ganoidei. |____________Dipnoi | | |__________________| | Proto-Ganoidei. | |____________Holocephali. | |____________Elasmobranchii. | Proto-Gnathostomata. | ____________________| | | _Cyclostomata_. | | | Proto-Vertebrata. | | | | ____________________|______________________ | | _Cephalochorda_. Protochordata. _Urochorda_. The hypothetical ancestral forms (Protochordata) possessed a notochord, a ventral suctorial mouth and numerous gill-slits, and were presumably descended from the common ancestor of Annelids and Vertebrates. Amphioxus and the Ascidians found their place in this schema as degenerate offshoots of the ancestral Protochordates, while the Cyclostomes were in the same way the degenerate modern representatives of the ancestral Protovertebrates. Balfour's suggestion, that the nervous system in Annelids and Vertebrates might have arisen by the dorsal or ventral coalescence of the lateral nerve cords found in their common ancestor, bore fruit in the speculations of Hubrecht,[409] on the relation of Nemertines to Vertebrates. The Annelid theory was firmly supported by Eisig, who in his elaborate monograph on the _Capitellidae_[410] maintained against Fuerbringer the genetic identity of the Annelidan nephridia with the kidney tubules of Vertebrates. The independent discovery by E. Meyer[411] and J. T. Cunningham,[412] of an internal segmental duct in _Lanice_, into which several nephridia opened, seemed to strengthen this view.