1880.] On the Cochlea of the Ornithorhynchus platypus. 149 



electrometer needle came to rest ; the result was that the residual 

 charge under these circumstances did not exceed 3 per cent, of the 

 original charge, also that it mattered not whether the discharge lasted 

 -rrs-oo" second or second. These experiments suffice to show that 

 neither of the above suppositions accounts for the facts. 



T have repeated my own experiments with the guard ring condenser, 

 but with a more powerful battery, and with a new key which differs 

 from the old one inasmuch as immediately after the condensers are 

 connected to the electrometer they are separated from it. In no case 

 do I obtain results differing much from those I had previously pub- 

 lished. 



Lastly, a rough model of the five plate induction balance used by 

 Mr. Gordon was constructed, but arranged so that the distances of the 

 plates could be varied within wide limits. So far as instrumental 

 means at hand admitted, Mr. Gordon's method was used. A plate of 

 double extra dense flint and a plate of brass were tried. In the first, 

 by varying the distances of the five plates, values of K were obtained 

 ranging from 1J to 8^, with the latter values from ^ to 3. It is clear 

 that the five plate induction balance thus arranged cannot give reliable 

 results. 



The explanation of the anomaly, then, is that the deviation from 

 uniformity of field in Mr. Gordon's apparatus causes errors greater 

 than anyone would suspect without actual trial. It is probable that 

 the supposed change of electrostatic capacity with time may be 

 accounted for in the same way. 



IV. " The Cochlea of the Ornithorhynchus platypus compared 

 with that of ordinary Mammals and of Birds." By Urban 

 Pritchard, M.D., F.R.C.S., Aural Surgeon of King's 

 College Hospital. Received November 9, 1880. Commu- 

 nicated by Professor Huxley, Sec. R.S. 



(Abstract.) 



General Form of the Cochlea of the Duckbill or Ornithorhynchus. 



This cochlea consists of a somewhat curved tube, about a quarter of 

 an inch (6 - 3 millims.) in length, and one-twentieth of an inch (T26 

 millim.) in diameter, projecting forwards from the cavity of the vesti- 

 bule and embedded in the substance of the petrous bone. It is nearly 

 horizontal, and is slightly curved outwards. 



In section the tube is first oblong, with its greatest diameter from 

 top to bottom, then somewhat triangular, and finally oval, with its 

 greatest diameter from side to side. It terminates in a slightly 

 enlarged rounded extremity, flattened from top to bottom. 



