DEVELOPMENT OF STJPRAPERICARDIAL BODY 371 



cases it completely disappears, leaving the bodies entirely 

 isolated. 



Histologically the bodies consist of small round follicles held 

 together by scanty connective tissue. The walls of these follicles 

 are formed of columnar or cubical epithelial cells which have 

 large round nuclei. The cavities of the follicles are filled with 

 a structureless mass containing an occasional nucleus. Van 

 Bemmelen was not able to find the nerve-supply and blood- 

 supply of the bodies, but thought that possibly their vascular 

 branches were derived from the truncus arteriosus or the axillary 

 artery. 



Van Bemmelen described the bodies in a number of species 

 of selachian embryos but was unable to find them in the mature 

 Heptanchus. In Chimaera the body develops behind the sixth 

 pouch, which completely degenerates. Often in Acanthias, 

 Scyllium, Pristiuris and Galeus the body develops only on one 

 side. In the Raia, Aetobatis, Acanthias and Chimaera the glands 

 remain until maturity and attain a considerable size. In Acan- 

 thias he describes and figures the duct-opening of the bodies in 

 the free surface of the pharyngeal mucous membrane on either 

 side of the copula. Van Bemmelen considers the supraperi- 

 cardial bodies as representing a rudimentary seventh pair of 

 branchial pouches which fail to reach the ectoderm and have 

 lost their original function. In support of this hypothesis he 

 argues that they are degenerate structures and are homologous 

 with epithelial derivatives of the spiracle and mouth in sela- 

 chians, which he also considers as rudimentary clefts. 



The same author ('89) continued the study of the supraperi- 

 cardial body or its homologues, in the higher vertebrates. He 

 found the body well developed in ganoids, amphibians and in 

 Lacerta. In Acipenser it consists of follicles as in elasmobranchs. 

 In one or the two examples of Acipenser studied the body was 

 found only on the left side. In amphibians the body is always 

 bilateral. It loses its connection with the pharynx very early 

 and develops into a relatively large, thin-walled cyst lying free 

 in the connective tissue. It remains as a simple cyst for a long 

 period, but ultimately sends out diverticula which develop into 



