286 INEZ L. VVH1PPLE. 



Moreover, it is also evident that with the lungs inflated and with 

 no muscular constriction of this posterior region this portion of 

 the body will possess greater relative buoyancy than the anterior 

 portion, or in other words the long axis of the body will assume 

 its ordinary position with the anterior end slanting downward. 

 As soon, however, as the ypsiloid apparatus is brought into 

 action, the resulting pressure upon the posterior abdominal 

 organs becomes exerted upon the clavate ends of the lungs thus 

 forcing the air in them forward. The effect is to immediately 

 increase the buoyancy of the anterior region of the body and 

 diminish that of the posterior region. 



On the other hand, when the muscles relax, the pressure of 

 the air in the lungs, as well as the elasticity of all the parts con- 

 cerned, causes the return of the air to the posterior region again 

 and the bulging of the body wall in this region occurs as before. 

 It seems probable that the superficial portion of the rectus 

 abdominis which is attached to the ventral side of the ypsiloid 

 cartilage (its fibers extending from the lateral arms to the stem 

 and to the anterior margin of the pubis), may assist in straighten- 

 ing the curved ypsiloid cartilage, since when the cartilage is in 

 the bent condition these fibers lie upon its convex (ventral) side. 



Thus the ypsiloid cartilage and the muscles connected with it 

 constitute, together with the lungs, the mechanism by means of 

 which the relative buoyancy of anterior and posterior ends of the 

 body may be controlled. One needs only to witness the constant 

 use of this hydrostatic apparatus by Dicinyctylits to understand 

 how completely the absolute ease of the animal under aquatic 

 conditions is due to its power to control the direction of its body 

 by means of the rapid adjustment of the relative buoyancy of 

 anterior and posterior ends. The ypsiloid apparatus is thus of 

 vital importance in the free-swimming aquatic life of a species 

 which, like Diemyctylus, depends for its food supply upon its ease 

 of movement in water at any depth. 



Opportunity has not been afforded me to study extensively the 

 aquatic activities of lunged forms other than Diemyctylus. Seve- 

 ral specimens of Ainblystoma punctatnui and Amblystoma opacum l 

 have, however, been observed with regard to this point. Both 



1 See p. 257 for statement with regard to the lungs of Amblystoma ofacimi. 



