Volume I 



NOVEMBER, 1912 



Number 6 



Labyrinth Fishes 



Part I 

 DR. E. BADE AND EUGENE SMITH 



A NIMAL life in the water and the distri- 

 ■i- -*- tribution of aquatic organisms depend 

 primarily on the oxygen content of the 

 water. It takes oxygen fully a day to pen- 

 etrate still water to a depth of only one-half 

 inch. With decreasing temperature of the 

 water the oxygen-holding capacity increases, 

 so that, for instance, at 20° centigrade (G8° 

 F.) it holds only half as much as at the 

 freezing point. 



Aquatic animals breathe the free oxygen 

 in the water through the body covering, their 

 trachea or their gills. The gills of fishes 

 are formed of rows of fine plates or lam- 

 inae, within which the many blood vessels 

 terininate as capillaries. Water is taken by 

 the mouth into the gill cavity and is dis- 

 charged again through the gill or opercle 

 opening, after passing over and through the 

 gills and there giving up its contained oxy- 

 gen to the blood. If there is lack of free 

 oxygen in the water the fish swim about at 

 the surface and get a direct supply of air, 

 which they gulp down mixed with the water 

 and so pass through the gills. Air which is 

 not used, as well as the expired carbon di- 

 oxide, is forced out at the gill openings in 

 the shape of bubbles. Most fishes die soon 

 after removal from the water, not olny be- 

 cause of the dryhig up of the gills, but also 

 because of the sticking together of the gill 

 tissue, thus causing a decrease of breathing 

 surface. 



Some fishes, however, are capable of 

 breathing atmospheric air directly, and so 

 are able to live in water from which all air 

 has been expelled, for instance, by boiling. 



These fishes, called labyrinth fishes, have 

 a special organ for air breathing called a 

 "labyrinth," an enlargement of the gill cav- 

 ity between head and body. This is a 

 bladder-like space or pocket extending back 

 into the dorsal skin. Within this pocket 



Head of labyrinth fish laid open to show "labyrinth' 



Fro7n Hjemmets Plaute og Dyrewordi-n, Copenhaseny No. 21 

 Ahgust, l'^12 



there is a laminate, coral-like, branched 

 and partitioned ossification of the first bony 

 gill arch, called the labyrinth bone. The 

 inner wall of the pocket and the bone itself 

 is lined with vascular tissue with numerous 

 fine blood capillaries and plexi. These 

 blood-supjilying vessels come from the gill 

 veins of the first gill arch, and the blood, 

 after passing through the labyrinth, where 

 it has become oxygenated in contact with 

 the air, flows back as arterial blood to the 

 heart through the veins of the head. Two 

 air-bearing vessels are connected with the 

 pocket, one opening out sideways from the 

 head at the upper edge of the gill cover, 

 the other opening into the rear of. the 

 mouth cavity and may be closed by a spe- 

 cial flap. It was formerly thought that the 

 labyrinth was a reservoir for holding water 

 to keep the gills constantly moistened Avhen 

 the fish breathed air. This vieAv, however. 



49 



