370 WALTER E. CAMP 



that such a study may help serve as a foundation upon which 

 to base in the future a more exact consideration of the homology 

 of this gland with similar structures in higher vertebrates. 



The present paper is based upon a study of a series of sec- 

 tioned embryos of Squalus acanthias from 19 to 95 mm. in 

 length and of sections and dissections of the glands of a number 

 of specimens of 'pups' (late fetuses), newborns and adults. Most 

 of the sectioned material is from the Harvard Embryological 

 Collection (H. E. C.) while some are from the embryological col- 

 lection of Dr. R. E. Scammon (S. C). The older specimens 

 were obtained from the Harpswell Biological Laboratory. 



I wish to thank Dr. Scammon for the loan of material and for 

 his continued interest and many helpful suggestions in the 

 progress of this work. 



LITERATURE 



The literature dealing with derivatives of the pharynx-wall 

 and gill-pouches of fishes and amphibians is very extensive. 

 Identical structures in the same species and homologous ones in 

 closely related forms have been given different names and inter- 

 pretations by various authors. The name 'suprapericardial body' 

 applied on this paper is the one originally given to the structure 

 by van Bemmelen ('85). 



Van Bemmelen ('85), in a study of the rudimentary branchial 

 clefts of elasmobranchs, describes the suprapericardial bodies 

 as a pair of small epithelial masses just caudal to the last pair 

 of branchial clefts. They extend through about half the thick- 

 ness of the ventral pharynx-wall which immediately overlies 

 the dorsal surface of the pericardial cavity. The bodies them- 

 selves begin to form in a stage when the last pair of clefts have 

 just opened. 



Originally the body is a simple evagination of the ventral 

 pharyngeal epithelium. Soon, however, its blind end expands 

 and forms a large ventral cyst. From the cyst small epithelial 

 sprouts arise which later acquire lumina arid become lengthened 

 and coiled. Usually the small neck or connecting-piece be- 

 comes stunted and remains as an excretory channel, but in some 



