662 FRANCIS M. BALDWIN 



paper, where she prefers to call them parathyreoids. In the only 

 urodele she studied (Spelerpes ruber), she found but a single body 

 on either side, and she does not trace its development, but merely 

 remarks on its small size (she was not able to find it with the 

 naked eye) and gives only a brief description of its histology. She 

 refers to Maurer in her account of the development (p. 101) of 

 this body in the anurans, but contributes nothing further of her 

 own. 



Morphology of the pharyngeal derivatives in other vertebrates 



As yet the problems of the homologies of the pharyngeal de- 

 rivatives in the different groups of vertebrates are not settled and 

 only brief statements of fact can be made here in the light of our 

 present knowledge. 



Thyreoid. This, of all pharyngeal structures, is the easiest to 

 homologize in the vertebrates, since, in all, it develops from the 

 epithelium of the floor of the pharynx. Whether it is paired or 

 unpaired, solid or hollow in its early anlage, and whether the mor- 

 phology, physiology and histology of the adult gland is the same 

 in all cases is not settled. Its development in the cyclostomes has 

 been recently followed by Reese ('02), Cole ('05), Schaffer ('06) 

 and Stockard ('06). In the ammocoete stage of the lamprey, it 

 retains its connection with the pharynx, and it was homologized 

 by W. Miiller ('71), with the endostyle of the tunicates. In the 

 later stage of the lamprey, as well as in the adult myxinoids the 

 duct is lost, and the gland becomes follicular and its parts scat- 

 tered in the region below the pharynx (Stockard, '06, in 

 Bdellostoma), 



In the elasmobranchs, Mrs. Thompson ('10) finds a compact 

 structure which she claims is partly epithelial, and partly adenoid 

 in character, and suggests that possibly the adenoid portion cor- 

 responds to the 'parathyreoids' of the higher vertebrates. In the 

 teleosts (Gudernatsch '11), it has the same tendency to become 

 broken into small isolated groups and scattered in the connective 

 tissue, and is not an anatomical unit and is therefore not a gland 

 in the sense of a compact structure. 



