8o CALIFORNIA ACADEMY OF SCIENCES. [3D Ser, 



straight forward in a line with the oral commissure, but 

 is projected ventralward, almost at an angle of 90 with 

 the commissure. This is caused by the vertical wall formed 

 by the premaxillary and maxillary bones which border the 

 mouth cavity from above, and by the fact that when the 

 water is forced out, the mouth is opened so slightly that the 

 entire outgoing current is brought against this wall and con- 

 sequently is deflected downward by it. 



The frequency of the respiratory movements varies some- 

 what, as would be expected, with the condition and tem- 

 perature of the water. Under ordinary circumstances one 

 counts on an average about ten expulsions of water per 

 minute. 



Apparently the animal does not usually come to the sur- 

 face of the water to get air, but to expel gas from its mouth. 

 When, under natural conditions, the need of discharging 

 gas is felt by the creature, it makes a sudden start for the 

 surface of the water, frequently swimming almost directly 

 upward. On the instant that the surface is touched by the 

 end of the snout, one or a few small bubbles of gas are dis- 

 charged from the mouth with a slight popping noise, and 

 the animal turns with a quickness quite in contrast to the 

 rather deliberate movements with which he executes the rest 

 of the process and swims back toward the bottom, frequent- 

 ly taking as direct a course as that by which he reached the 

 surface. The head is not usually thrust out of the water at 

 all, and almost the only visible indication on the surface of 

 what has taken place is the small bubble which is formed 

 and floats away for a short distance before it bursts. It is 

 these facts, viz., the nature of the contact of the snout with 

 the surface of the water, the discharge of the bubble of gas, 

 and the instantaneousness of the operation, that lead me to 

 believe no air is taken in. 



I am well aware that this conclusion does not harmonize 

 with that reached by Wilder ('76 and '77), Gage and Gage 

 ('86), and Mark ('90), from their experimental studies on 

 the respiration of Amia and Lej>ido$teous, soft-shelled turtles 

 (Amyda muttca and Asftidonectes sfiirifer), and Lepidos 



