78 Transactions. — Zoology. 



the skull at the apertures of the auditory capsules (fontanelles) 

 already referred to, to come into close contact with the lamina 

 of each fontanelle and thus to completely close them. To 

 quote from Professor Parker's paper in the " Transactions of 

 the New Zealand Institute, 1882 : " " Each cornu fits closely 

 against the three facets of the skull, and is strongly attached 



by fibrous tissue The arrangements described 



must form a fairly-efficient transmitting ajDparatus for the 

 organ of hearing. Sonorous vibrations, meeting the thin sub- 

 opercular skin, will be transmitted to the air in the aix'-bladder 

 and thence to the auditory fontanelle, the vibration of which will 

 act immediately on the perilymph. The subopercular skin will 

 thus act as an imperfect tympanic membrane, the air-bladder 

 as a tympanic cavity, and the auditory fontanelle as a, fenestra 

 ovalis." On the removal of the dorsal wall of the air-bladder, 

 in situ, there is noticeable a sort of cave, bounded anteriorly 

 by the button-like body already referred to. This cave thus 

 lies immediately posterior to the auditory fontanelle, and is 

 especially noticeable, because between the two caves (i.e., at 

 the median anterior part of the bladder), the dorsal, the an- 

 terior, and the ventral walls of the bladder are united and 

 thickened, forming a solid bar-like body. From that portion 

 of this thickened bar which lies mesiad of the two fontanelles 

 there passes backwards and outwards to the posterior and ex- 

 treme ends of each cornu a ridge formed as a thickening of 

 the dorsal wall of the cornu. The inner end of this ridge 

 forms the right or left — as the case may be — boundary of the 

 cave referred to. 



By this arrangement there is an imperfect partition between 

 the main body of the air-bladder and its cornua, and I would 

 suggest that the air-bladder is thus rendered a more perfect 

 tympanic cavity than it would otherwise be. At any rate, it 

 seems pretty certain that the ridge will, at least, have the 

 effect of conducting the sound-waves to the auditory fonta- 

 nelle. 



Given off from the ventro-lateral walls of the air-bladder 

 are a number of diverticula, which serve as means of attach- 

 ment. 



The rete niii-abilo extends forwards from about the middle 

 of the bladder. At its anterior end it passes outwards and 

 forwards in its own cornu. In a young specimen each retc 

 mirahile is a distinct band, and the anterior end^ — that con- 

 tained in the cornu — is separate from the posterior. In older 

 specimens the two bands have grown together in the middle 

 line, and the break at the anterior end is almost obliterated. 



Urino-genital Organs. — The kidneys lie on the dorsal sur- 

 face of the abdomen above the air-bladder, one kidney lying 

 on each side of the vertebral column. They consist of two 



