372 WALTER E. CAMP 



small independent follicles. He did not find the body in tele- 

 osts. In Lacerta the body is present only on the left side and 

 lies much farther forward than it does in selachians and am- 

 phibians. Histologically it is very similar to that found in 

 Amphibia. In birds and mammals van Bemmelen found great 

 variation in the pharyngeal derivatives of the cervical region in 

 the different forms. He homologizes with the suprapericardial 

 body of selachians, the 'accessory trryreoids' of De Meuron in 

 birds and mammals; the 'postbranchial bodies' of Maurer in 

 amphibians; the 'Body Y' of Mall in birds; and the 'lateral 

 thyreoids' of Born and His in mammals. 



In a study of the pharyngeal derivatives in the higher forms, 

 van Bemmelen urges great care in differentiating between those 

 which arise from the pouches themselves and those which spring 

 directly from the pharynx-wall. This is particularly true in 

 mammals, where these derivatives, although very similar in 

 structure, are to be distinguished by their mode and place of 

 origin. He believes that the suprapericardial bodies in reptiles 

 and their homologues in birds and mammals, as in the selachians 

 and amphibians, represent a rudimentary pair of branchial 

 pouches. 



De Meuron ('86), in his studies on the development of the 

 thymus and thyreoid glands, gives a brief account of the supra- 

 pericardial body in selachians and amphibians. He homolo- 

 gizes the body in these forms with the accessory thyreoid of 

 reptiles, birds, and mammals. 



In Acanthias vulgaris (Squalus acanthias) De Meuron describes 

 the suprapericardial body as a small diverticulum, arising from 

 the ventral pharynx-wall, caudal to the last branchial cleft. 

 Although the body may, primarily, arise symmetrically on the 

 two sides, only the one on the left continues to develop. The 

 right body rapidly atrophies and completely disappears. The 

 left body, later in its development, separates from the pharynx, 

 and divides into many small follicles. 



In amphibians (Rana and Bufo) the bodies arise symmetri- 

 cally on the two sides of the pharynx, caudal to the branchial 

 clefts. Here the bodies always separate completely from the 



