408 WALTER E. CAMP 



He also believes that the ultimobranchial body in man does not 

 represent a vestigeal ancestral gland, and that, with the possible 

 exception of the ultimobranchial body of birds, no gland has 

 been found in the forms below mammals with which the ultimo- 

 branchial body may be homologized. If we admit the conten- 

 tion of Kingsbury that the ultimobranchial body in man is 

 branchiogenetic in its origin, then it would appear without 

 justifiable doubt that this structure could be homologized with 

 similar branchiogenetic organs in lower forms, including the 

 suprapericardial body of selachians. The distinction of whether 

 the gland in question develops from a degenerating pouch or 

 simply from the epithelium which has the potentiality of form 

 ing a rudimentary pouch seems to me to be unnecessary. The 

 more recent work on the ultimobranchial body by Badertscher 

 ('16) in the pig tends to show that these bodies do not degenerate 

 entirely, but contribute to the formation of the structural ele- 

 ments in the thyreoid gland. 



SUMMARY 



1. The suprapericardial body of gland in Acanthias appears 

 in embryos of about 20 mm. in length. It arises as an out- 

 pouching of the epithelium of the ventral pharyngeal wall, medial 

 and slightly caudal to the sixth gill-pouch. In its position and 

 mode of development the gland corresponds to the ventral ex- 

 tremity of a rudimentary seventh pouch. 



2. The epithelial outpouching forming the anlage of the gland 

 rapidly develops into a solid connecting-stalk and a blind, ex- 

 panded ventral portion. The dorsal part of the connecting- 

 stalk remains as a diverticulum from the pharyngeal epithelium. 

 The remaining part of the connecting-stalk and the expanded 

 ventral portion of the gland become converted into large, dis- 

 tended vesicles, most of which intercommunicate, but some of 

 which are completely isolated. A part of the gland in the adult 

 may secondarily become connected with the pharynx by a true 

 duct. In its development and structure, therefore, the supra- 

 pericardial body represents a type of gland intermediate in 



