DEVELOPMENT OF SUPRAPERICARDIAL BODY 375 



scribed the fifth pouch as the last, and considered the derivatives 

 of the rudimentary sixth pouch as postbranchial structures. 



Greil also opposes the view of Maurer and De Meuron that 

 the suprapericardial body in Anura develops as an outpouching 

 of the pharyngeal wall. On the contrary he describes it as a 

 solid thickening of the epithelium which develops a central 

 lumen after its separation from the pharynx. He thinks that 

 De Meuron has described the body in a fairly advanced stage 

 of development — after the formation of a central lumen — and 

 has mistaken this for its earliest anlage. Greil was unable to 

 find the suprapericardial bodies in five specimens of Bombinator 

 studied by him. 



In selachians, Greil found the ultimobranchia] body only on 

 the left side. In Acanthias he describes the anlagen of the 

 seventh pouches arising caudal and medial to the sixth pouches. 

 The appearance of the seventh pouches is delayed by an eleva- 

 tion of the pharyngeal wall in the region of the sixth pouches. 

 On the medial side of this elevation the ventral extremity of 

 the seventh pouch on the left side develops into the ultimo- 

 branchial body. 



Greil agrees with van Bemmelen that the ultimobranchial 

 (suprapericardial) bodies represent rudimentary seventh pouches, 

 especially their ventral extremities. He thinks that in Chi- 

 maera — in which the suprapericardial bodies are formed behind 

 the sixth pouches (which degenerate without leaving any deriva- 

 tives) — it is very probable that the loss of the sixth pouch is to 

 be considered as a unique case, and a phenomenon to which the 

 suprapericaridal body has not yet adapted itself, as it has, for 

 example, in the amphibians. In this latter group the formation 

 of the suprapericardial body is assumed by the sixth pouch. 

 In the higher groups, in which the reduction of the gill apparatus 

 is more advanced and in which there are only four pouches, the 

 suprapericardial body is formed from the last pouch. 



Vialleton ('08), in his work on the visceral arches in verte- 

 brates, describes briefly the suprapericardial bodies in Torpedo. 

 In large embryos of this form (70 mm. in length) they consist 

 of a short excretory canal closely surrounded by a few glandular 



