76 



BALANOGLOSSIDA. 



apertures are, except in Ptychodera and Stereobalanus canadensis, 

 tubes, which lead outward to open externally by the branchial 

 pores placed in the branchial groove on each side of the middle 

 dorsal line. The internal openings (gill-slits) are U-shaped, the 



ion 



FKJ. 61. Glossobalanus minutus, transverse section through the branchial region, somewhat 

 diagrammatic (after Spengel from Lang). 1 dorsal nerve cord ; 2 dorsal blood-vessel ; 3 bran- 

 chial (submedian) groove ; 4 ectoderm ; 5 gonad ; 6 longitudinal muscles of body- wall; 7 ven- 

 tral vessel ; 8 ventral nerve cord ; 9 trunk coelom ; 10 genital pore ; 11 branchial pore ; 12 

 tongue bar containing extension of trunk coelom ; 13 parabranchial ridges ; 14 primary or 

 septal bar, i.e. portion of wall of pharynx intervening between two successive clefts ; 15 

 dorsal part of cavity of pharynx ; 16 hypobranchial groove of pharynx, in this region 

 very largely developed. 



dorsal margin having a tongue-like projection, forming a tongue- 

 bar (Figs. 60, 62) as in Amphioxus. This leads into a pouch 



canal with the food to escape. On this view, the skin, which contains a 

 rich plexus of blood vessels, would act as the main organ of respiration. 



