1871.] 125 [Dall. 



tion, equally good, which shall include the Brachiopods with the An- 

 nelids Tunicata and Pohjzoa as opposed to the typical Mollusks. 

 This he has yet failed to do. 



Mr. Morse seems to think that I have omitted the unisegmental 

 "vermes" in my comparison. I have not considered /'segmenta- 

 tion," as properly understood, as a character at all. Segmentation 

 is merely an adjunct, and the successive repetition jof organs occurs 

 without it, throughout the worms. The set® of Brachiopods, some- 

 times entirely absent, are not arranged in successive series as are the 

 setae of worms. Furthermore, I have expressly avoided drawing any 

 homology between the peduncle of Lingula and the siphon of Mya, 

 but have pointed out that the histological structure of the two being 

 identical it affords no basis for homologizing the peduncle of Brachio- 

 pods alone with any Annelidan organ. Nor have I stated or inferred 

 anywhere, that the position of the setae in Brachiopods prevents 

 their identity in structure with those of Annelids, but I have proved 

 that their structure is by no means identical, and any homology 

 drawn from them is therefore erroneous. 



I am at a loss to know the basis of the remark that I believe all 

 Chaetopods have setae from head to tail, and trust that the inferences 

 which Mr. Morse has drawn from certain supposed characters of 

 Brachiopods are less erroneous than those which my paper appears to 

 have afforded him. 



In regard to Chitons, admitted to be Mollusks, though a very aber- 

 rant group, I have shown that their aberrancies are in some points 

 similar to those of the Brachiopods, and therefore should not be 

 taken in either as proofs that either group is non-Molluscan. Such 

 homologies would afford a much more powerful argument for placing 

 the Tunicates among the Vertebrates than any yet brought forward 

 by Mr. Morse for placing the Brachiopods with the Worms. 



Leuckhart, Gegenbaur and Haeckel, have, it is true, placed the 

 Polyzoa and Tunicata among the "Vermes," but their views have 

 not been adopted by naturalists, and proceed, as in my opinion do 

 those of Mr. Morse, from a magnifying of certain unimportant char- 

 acters and the overlooking of truly valid details of structure. 

 Proofs have not been afforded of either view ; when they are, it will 

 be time to combat them. 



With regard to the embryology of the Polyzoa, Tunicata and 

 Brachiopoda it must be remembered that they differ among them- 

 selves in this regard, as widely as do any of the higher subkingdoms, 



