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branchial portion of the pharynx. Dependent upon the answer to this 

 question is the decision as to its designation als ultimobranchial, telo- 

 branchial, or postbranchial. (2) Its fate; whether or not it persists 

 within the thyroid and contributes to that organ any structural elements. 

 (3) Its value and interpretation as an organ or a structure. 



To this last question Grosser has attempted an answer in his 

 paper of 1910. He then decided that (p. 337) "the ultimobranchial 

 body clearly represents a ductless gland which has become rudiment- 

 ary", and concluded that ''from what has been presented the justifi- 

 ableness of interpreting the ultimobranchial body as a special gland can 

 no longer be disputed." The interpretation of Grosser's is in ac- 

 cordance with what might be termed the "colony conception" of the 

 bodily organization, — as an aggregation of individually distinct organs 

 possessing specific functions. The occasional appearance of epithelial 

 structures within the thyroid probably referrable to this pharyngeal 

 derivative as a source of origin, upon the above basis, calls for the 

 assumption of some specific organ in an ancestral past which it 

 specifically represents. There seem to me to be two main objections 

 to the interpretation made by Grosser both from the comparative side. 

 The first of these is that, with the possible exception of the ultimo- 

 branchial body of birds, no gland has been found in the forms below 

 mammals with which the ultimobranchial body may be homologized. 

 The second objection is that ultimobranchial bodies, — if we use that 

 term, — of the different classes of vertebrates cannot themselves be 

 directly homologized. Greil '05 gave evidence that this structure in 

 anurous amphibia developes from a last branchial pouch, and to him 

 we owe the name 'ultimobranchial'. Tandler '09 from his studies 

 of an extensive series of human embryos has concluded that this 

 pharyngeal derivative is an ultimobranchial body and represents a 

 vestigial fifth pouch, and Grosser has so far followed him in his 

 interpretation as to consider it a derivative of or belonging to a fifth 

 pouch. It is obvious that upon the interpretation of the ultimo- 

 branchial body as a branchiomeric organ, as a derivative of a rudi- 

 mentary fifth pouch, — the 'ultimobranchial' structures of lower verte- 

 brates cannot represent it, since the fifth pouch may be a functional 

 gill pouch in the amphibia. H. Rabl in a discussion at the 1911 

 meeting of the ''Anatomische Gesellschaft" suggested that the ultimo- 

 branchial body of mammals represents a fifth and sixth pouch. More 

 recently (1913) he has homologized it in the guineapig with a sixth 



