8 



THE POPULAR SCIENCE MONTHLY. 



markable for the large quantity of air which escapes from its mouth. 

 The source of this air he has not been able to determine. At certain 

 times it approaches the surface of the water, and seems to take in 

 air, but he could not think that so large a quantity as is seen adhering 

 in the form of bubbles to the sides of the gills could have been 

 swallowed, nor could he suppose that it could be secreted by the gills 

 themselves." 



Since the exhalation of air from any source is evidently as easily 

 performed below the surface, the periodical ascent of the gars goes 

 far to show that there is likewise an inhalation. But as it was not 

 easy to determine this, on account of the small size of the young gars 

 and the difficulty of handling the older ones, the writer experimented 

 upon another Western Ganoid, the Amia, or " mud-fish," or " doo-- 

 hsh." 



When i^laced in a tank the Amia kept near the bottom, and 

 seemed to prefer the darker portions. But it came to the surface at 

 pretty regular intervals, emitting one or two large bubbles from the 

 mouth, and, on descending, several smaller ones from tlie opercular 

 orifice. 



The fish was gradually accustomed to having the body gently em- 

 braced by the hand about the middle. 



Fig. 4. Vertical Longitudinal Section op the Head op Lepidosteus platystomus. One- 

 half Natural Diameter. 



Br, the brain cut on the median line po as to show the ventricles of the two hinder lobei, the 

 cerebellum and optic lobes. SC, the spinal cord passino; backward into the canal of the ver- 

 tebral column ( Tx'). CT. a mass of connective tissue filling the hinder part of the brain-cav- 

 ity. HP. the right hyi)opharyngeal bone, just in front of the passage XCH) from the throat 

 {Al) upward and backward into the air-bladder {A). Ve is a valve which seems to guard_ the 

 opening from within ; a corresponding valve is on the left side. LA is one of the openings 

 from the median channel of the air-bladder into a lateral chamber. X is the liver, which ter- 

 minates forward in a large blood-vessel, BV- A and Fare the auricle and ventricle of the 

 heart ; BA, the branchial artery; and ba, the cut ends of the smaller arteries to the gills on the 

 right side. T is the tongue. 



Having been thus prepared, the fish was permitted to swim to and 

 fro in the tank, but prevented from rising. It soon became uneasy, 

 and, after a few not very violent efforts to disengage itself, emitted a 

 large bubble of air. 



Now, if this emission were all that was necessary we may suppose 

 that it would have remained quiet for another period. On the con- 

 trary, after a second or two of repose (perhaps resulting from the 

 habit of being satisfied after the respiratory act), the fish became more 

 and more uneasy, moved rapidly to and fro, turned and twisted and 

 lashed with its tail, and finally, by a violent effort, escaped from the 

 hand. It rose to the surface, and, withovt emitting any bubble, opened 



