. Elementary text-book of zoology. Zoology. RESPIRATORY ORGANS. 145 remnant of a gill—the pseudobranch of the spii-acle—the vessels of which belong to the arterial circulation and form a rete mirabile. In the Teleosteans (fig. 593 6) and the Ganoids the lancet-shaped lamella? are arranged in double rows on the four visceral arches which func- tion as branchial arches, and they form four comb-shaped gills on either side. These gills lie in a spacious branchial cavity covered by the branchial oper- culum and the branchial membrane. There is, however, an accessory gill on the inner side of the br
. Elementary text-book of zoology. Zoology. RESPIRATORY ORGANS. 145 remnant of a gill—the pseudobranch of the spii-acle—the vessels of which belong to the arterial circulation and form a rete mirabile. In the Teleosteans (fig. 593 6) and the Ganoids the lancet-shaped lamella? are arranged in double rows on the four visceral arches which func- tion as branchial arches, and they form four comb-shaped gills on either side. These gills lie in a spacious branchial cavity covered by the branchial oper- culum and the branchial membrane. There is, however, an accessory gill on the inner side of the branchial oper- culum; this in many Ganoids and Ohimsera functions as a gill, but in the Teleosteans has lost its respiratory function, and is then known as the pseudobranch of the operculum or of the hyoid arch. External gills projecting from the slits of the branchial pouches are found only in the embryos of the Plagiostomes. Rudiments of external gills are found in Rhinocryptis annectens. Finally the secondary cavities, which are sometimes found annexed to the branchial cavity and increase the re- spiratory surfaces by the development of a capillary network, must be regarded as accessory organs of respiration. They consist either of labyrinthine cavities in the superior pharyngeal bones (fig. 594) or of saccular appendages of the FlG. circulation branchial cavity (Saccobranchus, Am- phipnous). True lungs derived from the swimming bladder, with internal cellular spaces, a short air-tube and glottis-like opening into the pharynx, are only found in the Dipnoi (according to Hyrtl the swimming bladder of Gijmnarchus is also a lung). Vascular system.—The blood is generally red; it is white only in A mphioxus and the LeptocephaMdce; it circulates in a closed VOL. II. 10. of aTeleostean. I', ventricle ; Ba, bulbus arteriosus with the arterial arches which carry the blood to the gills ; Ab, arterial arches; Ao, aorta descenclens into which the epibranchial arte
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1884
