Annelids

Gill-slits, notochord, relation of nervous system, mesonephric tubules, are thus common to Annelids and Vertebrates -- what further proof could one desire of the close relationship of these groups?

Form and Function A Contribution to the History of Animal Morphology

But he has still to show that Annelids possess at least the rudiments of certain organs which seem to be peculiar to

Form and Function A Contribution to the History of Animal Morphology

Not content with establishing the unity of plan of Annelids, Arthropods, and Vertebrates, Semper tries to link on the Annelids, as the most primitive group of the three, to the unsegmented worms, and particularly to the Turbellaria.

Form and Function A Contribution to the History of Animal Morphology

Both Dohrn and Semper started out from the fact that Annelids and Vertebrates are alike segmented animals, and it was an essential part of their theory that this resemblance was due to descent from a common segmented ancestor.

Form and Function A Contribution to the History of Animal Morphology

Semper, took up a distinctly favourable attitude to the general idea that Annelids and Vertebrates were descended from a common segmented ancestor.

Form and Function A Contribution to the History of Animal Morphology

Amphioxus, he thinks, is not a Vertebrate, and Ascidians, though sharing with Annelids the possession of a notochord, gill-slits, and a "dorsal" nervous system, yet are further removed from Vertebrates than the latter by reason of their lacking that essential characteristic of Vertebrates, metameric segmentation.

Form and Function A Contribution to the History of Animal Morphology

He will not admit that Amphioxus and the Ascidians show a closer resemblance to Vertebrates than his beloved Annelids.

Form and Function A Contribution to the History of Animal Morphology

Annelids by the "giant-fibres" or neurochordal strands which lie close above the nerve-cord, a view held by Kowalevsky, [414] and for a time by

Form and Function A Contribution to the History of Animal Morphology

The gill-slits were considered by Dohrn to be derived from the segmental organs of Annelids, which were present originally in every segment of the primitive ancestor.

Form and Function A Contribution to the History of Animal Morphology

Much difference of opinion reigned as to the true homologies of the brain and mouth of Annelids and Vertebrates.

Form and Function A Contribution to the History of Animal Morphology