EAR-SWIMBLADDER RELATION IN CLUPEOIDS 223 



of its development, the diverticulum is structurally a continu- 

 ation of the mucosa (tunica interna) of the swimbladder, and is 

 made up of corresponding layers. The epithelium of the swim- 

 bladder continues from its anterior end (here simple squamous) 

 into the diverticulum, where it becomes columnar and is thrown 

 up into simple folds which suggest a glandular structure (fig. 1). 

 In the parts of the diverticulum inside the bones of the skull, 

 the epithelium becomes low cuboidal or squamous and is not 

 thrown up in folds (Stolephorus and Pomolobus). The epithe- 

 lium of the membranous vesicles is simple squamous (fig. 17). 

 The tunica propria in the tubular part of* the diverticulum is 

 thin but dense and at the beginning of the diverticulum in 

 Stolephorus contains a layer of circular smooth muscle. Very 

 loose, sparse connective tissue (submucosa) suspends the tube 

 in the cartilage canal (fig. 1). The connective tissue attach- 

 ing the membranous vesicles to the inner surface of the osseous 

 capsules is very loose; here the tunica propria and submucosa 

 blend into each other. 



The posterior membranous vesicle of the swimbladder diver- 

 ticulum, which lies in the posterior osseous capsule, is practi- 

 cally the same in structure as that of the anterior membranous 

 vesicle. Since the posterior vesicle has no apparent relation to 

 the labyrinth or other structure outside the bony capsule, it will 

 not be discussed further in this paper. 1 



The cartilage tube around the diverticulum is continuous 

 with the tunica externa of the swimbladder and is probably the 

 morphological representative of that layer. The cartilage in 

 Stolephorus and Pomolobus presents, in sections, a somewhat 

 peculiar microscopic appearance, since the cartilage cells are 

 larger than usual in comparison with the amount of intercellular 



1 The development of this vesicle is almost unknown. It is not formed until: 

 comparatively late stages. It is not present in Stolephorus or Brevoortia in 

 specimens earlier than 30 mm. in length. It is, however, fairly well developed 

 in a young Stolephorus 38 mm. in length. The relations shown in this specimen 

 indicate that it develops by the formation of an outgrowth from the main branch 

 of the precoelomic diverticulum. This outgrowth pushes up into the space 

 within the canal for the diverticulum in the otic capsule (indicated by the end of: 

 the reference line CSD in fig. 15). 



