REPORT OP THE SECRETARY. 15 



" The air sacs of the pigeon," by Bruno Miiller, was published during 

 the past year in the Smithsonian MisceHaneous Collections. The au- 

 thor summarizes the conclusions of his studies as follows: 



I do not consider the air sacs, including the air cavities of bones, as organs 

 having a positive and special function, but rather as a system of empty intei*- 

 spaces. Their value lies in their emptiness — that is, in their containing nothing 

 that offers resistance or has an appreciable weight. 



Flying is the highest form of locomotion, and as such only possible to a body 

 of high mechanical efficiency. Our most effective machines are by no means 

 compact and solid, but composed of parts as strong as possible in themselves 

 and ari-anged in the most appropriate manner. The interspaces between the 

 parts are left empty and taken up by air. 



The Sauropsida, at the time they obtained the power of flight, became adapted 

 to its mechanical requirements, and thereby similar to the eflicieut machines 

 mentioned above; they divested themselves of all superfluous material, filling 

 the body spaces thus obtained with air sacs. While the body wall, adapting 

 itself to the mechanical requirement, became a compact, hollow cylinder serving 

 as a support for the organs of movement, the mobility of the parts was assured 

 by surrounding them with air sacs. 



The lengthening of the neck, produceil by quite a different adaptation, made 

 necessary an increase in the quantity of air moved during respiration. This 

 demand was met by air currents generated through a rhythmical change in 

 the volume of the air sacs. The connection of the air sacs with the lungs is a 

 consequence of their phylogenetic development, which is repeated in their 

 embryological development, and has no physiological significance other than 

 that the air sacs assist in renewing the air in the trachea. 



MECHANICS OF THE EAETH's ATMOSPHERE. 



Prof. Cleveland Abbe, who has received a Hodgkins grant for the 

 pref)aration of a second volume of translations of important foreign 

 memoirs on the mechanics of the earth's atmosphere, has about com- 

 pleted this work. The former collection of translations on this sub- 

 ject by Professor Abbe, published in 1891 as volume 34 of the Smith- 

 sonian Miscellaneous Collections, has been widely used and recognized 

 to be of important service to those engaged in the study of modern 

 dynamic meteorology. 



NAPLES ZOOLOGICAL STATION. 



For the past fifteen years the Smithsonian Institution has supported 

 a table at the Naples Zoological Station and offered its facilities for 

 study to biologists recommended by an advisory committee of emi- 

 nent specialists. During the past year I have been aided by the 

 prompt and helpful action of this committee, whose membership con- 

 tinues the same as heretofore. 



The occupation of the Smithsonian table was approved on behalf of 

 Mr. J. F. Lewis, of Johns Hopkins University, for the month of 

 March, 1908. His actual stay, however, exceeded that period by some 



