THE YPSILOID APPARATUS OF URODELES. 287 



of these species, although capable of much less perfect adjust- 

 ment to aquatic life, resemble Diemyctylus in the fact that the 

 lungs are used as hydrostatic organs. Almost the first act of an 

 Amblystoma when it is placed in deep water is to swim to the top 

 and take in the air sufficient to float the body. I have not ob- 

 served an Amblystoma opacum to become sufficiently at home in 

 the water to do more than to remain floating at the surface. 

 Amblystoma punctatnm will, however, after a little while, appear 

 quite at ease, crawling about the bottom, floating at the surface, 

 or swimming around with much freedom. 



Although the greater thickness and breadth of the rectus 

 abdominis of Amblystomas prevent the visible exhibition of the 

 action of the ypsiloid region during aquatic life, changes of shape 

 of the posterior lateral walls of the body are often observable. 

 Upon one occasion a specimen of A. pnnctatnin was observed 

 floating in a horizontal position at the surface of the water. Sud- 

 denly there was a violent contraction of the posterior abdominal 

 walls particularly noticeable in the lateral region, and immediately 

 the position of the body became so nearly vertical that the head 

 was sufficiently protruded from the water to make aerial respira- 

 tion through the nostrils possible. This observation not only 

 proved that the ypsiloid apparatus is functional in the control of 

 the hydrostatics of Amblystoma punctatum, but it suggests the 

 application of its action as a means for bringing the floating body 

 into such a position that the respiration of air may occur. In the 

 case of imperfectly aquatic forms this use of the mechanism might 

 at times be extremely important. For example, Amblystoma 

 opacum will frequently, if compelled to remain in the water, take 

 this same almost vertical position at the surface with the nostrils 

 out of the water and is thus able to breathe air. 



That the lungs of Amblystomas are of greater importance as 

 respiratory organs than are those of Diemyctylus is evidenced by 

 the fact that they are more complicated in structure and there- 

 fore present a much larger respiratory surface. They are, how- 

 ever, like the lungs of Diemyctylus, of sufficient length when 

 moderately inflated to extend the entire length of the body cavity 

 and would therefore lend themselves readily to the hydrostatic 

 function in connection with the ypsiloid apparatus. 



