532 Recently published Ornithological Works. 



difficulties and is by no means yet exhausted. His investi- 

 jiations Avere carried out in the Zoological Laboratory of the 

 German University at Prague, the author being assisted to 

 prosecute his researches out of the Hodgkins Fund of the 

 Smithsonian Institution. 



Without doubt this is the most complete account of the 

 air-sacs of birds which has yet been written, and it is illus- 

 trated by some really beautiful figures representing the 

 author's dissections. The study of these air-chambers is 

 one of quite exceptional difficulty, and the author must be 

 congratulated on the marvellous success which he has 

 achieved. 



Although he has carefully studied the literature of his 

 subiect, and does ample justice to the pioneers in this branch 

 of avian anatomy, Mr. Miiller has omitted reference to 

 one or two comparatively recent memoirs, which is the 

 more to be regretted because his opinion thereon would have 

 been valuable. 



This paper is much too long to make a detailed account 

 thereof possible, but reference may fittingly be made to his 

 criticisms of the surmises of other investigators as to tlie 

 function of these remarkable receptacles, and to his own 

 conclusions as to their purpose. 



Of recent theories as to the function of these air-chambers, 

 that which supposes them to serve in part as regulators of 

 temperature, and in part, and chiefly, as accessory respiratory 

 oro^ans, finds most general acceptance at the present day. 

 In avian respiration, in short, it is generally believed that 

 the air is drawn swiftly through the lungs into the air-sacs, 

 from which it is slowly forced back into the lung-capillaries. 

 To this view the author objects, contending that the air forced 

 from the air-sacs into the lungs would, after losing a portion 

 o£ its oxvgen, pass back again into the sacs. But this is a pure 

 assumption, unsupported by any facts whatsoever. Rather, 

 the heavier deoxygenated air would be driven forward 

 through the lung to the trachea by the pressure of the lighter 

 newly-inspired oxygenated air which would rush in to occupy 

 the place of the air as it is expelled from these chambers. 



