DEVELOPMENT OF SUPRAPERICARDIAL BODY 



403 



we are justified in assuming that in Acanthias the supraperi- 

 cardial body represents the ventral extremity of a rudimentary 

 seventh gill-pouch. In many of the specimens which I have 

 examined, the gland in its early stages appeared like a rudimen- 

 tary pouch which had become stunted in its progress of growth 

 by abutting against the underlying pericardial wall. 



The failure of the gland to appear on the right side in many 

 of the specimens is difficult to explain. From my material it 



Fig. 19 Semidiagrammatic section through the pharynx of an embryo 28 mm. 

 long (S. C. 6) at the level of the left suprapericardial body. X 40. Ao., aorta; 

 V,VI, fifth and sixth gill-pouches; P.c, pericardial cavity; s.b., suprapericardial 

 body. 



appears to be the rule rather than the exception that the right 

 body fails to appear. Van Bemmelen ('85) found that often in 

 Acanthias, Pristiuris and Galeus the body appears only on the 

 left side. He figures a dissection of the 'pup' stage showing the 

 openings of the gland on either side of the cardiobranchial carti- 

 lage. Although numerous specimens of the 'pup' were exam- 

 ined, I found the gland only on the left side (fig. 29). All of 

 these specimens however were not sectioned and possibly in 

 some cases the right gland was present, but too small to be seen 

 with the binocular microscope. De Meuron ('86) says that in 



