658 FRANCIS M. BALDWIN 



tral floor of the pharynx on either side, not posterior to the fifth 

 pouch (as was described by Maurer) , but between the fourth and 

 fifth pouches. Thus, the position of the body in Necturus as 

 described by her, opposes the view of van Bemmelen, on the one 

 hand, that they be regarded as 'rudimentary branchial clefts,' 

 and that of Maurer, that they are ' postbranchiaF on the other. 

 She therefore prefers to call them ' suprapericardial' rather than 

 'postbranchial.' 



Maurer ('02), p. 143, briefly reviews the development of the 

 structure in the amphibians, and while he contributes no new 

 evidence of his own, he emphasizes the fact that it is to be re- 

 garded as a ' postbranchial ' structure. He says, "Da er hier 

 hinter der letzten Kiemenspalte liegt, eine Beziehung zum Peri- 

 card nicht besteht habe ich das Organ als postbranchialen Korper 

 bezeichnet. Er liegt stets hinier der letzten Kiemenspalte mag 

 diese nun die 4, 5 oder 6 sein." 



Driiner ('04), p. 508, describes the postbranchial body in but a 

 single stage of Siredon (3.6 cm.) where it was a small ampulla- 

 like structure, on the left side only, formed by the insinking of the 

 pharyngeal epithelium. In other series of the same form, he 

 failed to find it. 



Greil ('05) describes its development in Rana, Bufo and Hyla, 

 and disagrees with Maurer's view that it is 'postbranchial,' since 

 it arises from the ventro-caudal region of a rudimentary sixth 

 pouch, and is thus ' ultimobranchial. ' The early anlage, accord- 

 ing to him, is not formed by an out-pocketing of the pharyngeal 

 epithelium, but by a simple thickening, which later develops a 

 lumen. He agrees with van Bemmelen, that in the selachians, 

 the body represents a rudimentary seventh pouch, but in the 

 amphibians, where the seventh pouch is lost, the formation of the 

 structure is assumed by the sixth, and so on in the higher groups 

 as in mammals, the formation of the body is assumed by the last 

 gill-pouch, the fourth. 



In Hypogeophis, Marcus ('08), finds that the body develops 

 symmetrically, but is derived from the seventh pout3h instead of 

 the sixth as in the other amphibians ; the sixth in this form appar- 

 ently degenerating (see p. 733). He retains the name 'ultimo- 



