REPORT OP THE SECRETARY. 67 



• 

 In connection with the building of the fence it became necessary to reestablish 

 certain points on the boundary line where the grading of District highways had dis- 

 placed the original marks or where the line had been altered since the official sur- 

 vey was made. The surveyor of the District of Columbia was accordingly employed 

 to resurvey the boundary and prepare a new and authoritative map. 



Bear yards. — Two bear yards begun at the close of the previous year have been 

 completed. Provision has been made for a series of 10 yards, and the site for the 

 entire series has been graded. The two central cages of the series were built and are 

 occupied, respectively, by the Kodiak bear and the pair of polar bears. These cages 

 are approximately 40 feet square, and each contains a bathing pool about 20 feet in 

 diameter. The fence is 10 feet high, with an overhang inward of 2 feet 6 inches. It 

 is constructed of vertical bars of |-inch stiff round steel, spaced 5 inches on centers, 

 passing through horizontal rails of 2 J by | inch round-edged steel. Each yard is 

 provided with a house in the rear, the front of which is of large weathered rocks laid 

 up with wide irregular joints. Rear walls are of concrete. Each house has a grating 

 door at front and rear and a grating across one end the entire width of the house. 

 In winter a tight storm door is lifted into the rear opening, and the open end of the 

 house is closed with a wooden panel. The door at the front is closed with a sliding 

 grating, operated outside the house. There is also a grating door at the rear of the 

 yard for the use of keepers, all attendance being from the rear. The cost, including 

 grading, drainage, and water supply, has been $3,000. Trees have been planted 

 about the cages, which after a few years will shade both animals and visitors. A 

 trellis of light steel framework has been constructed over the public walk and the 

 front part of the cages, and over this quick-growing vines are being trained, which 

 will afford shade till the trees reach sufficient size to render such shade unnecessary. 

 Eagle cage. — This structure«also was begun as the last fiscal year ended. It was 

 completed early in the present year and at once occupied. The cage has proved to 

 be very satisfactory, and it is hoped that in the near future similar structures can be 

 built for other birds of prey, especially for the California condors, which now have to 

 be kept in a cage of quite inadequate size. 



The following alterations and additions have been made to buildings and grounds 

 during the year: 



Iniprorcmenta in aquarium. — The small aquarium maintained for several years in 

 an old work shed proved to be of so much interest to visitors that it seemed advisa- 

 ble to make some alterations in order to provide more satisfactory conditions for 

 operation and exhibition. Under your instructions the lighting, which had been 

 insufficient, was improved by putting in a continuous series of skylights on the north 

 side and doubling the skylight area on the south side. A new exhibition tank, 12 

 feet long, 3 feet 10 inches high, and 5 feet deep, was constructed at the end of the 

 corridor. A second concrete storage tank for salt water was built and an extra pump 

 and additional piping put in, so that the entire series of tanks on one side and the 

 new end tank can be supplied with salt water. It was also recognized that a bare 

 background of asphalted wood did not display fishes to advantage or give any proper 

 idea of the surroundings in which they ordinarily live. Some of the tanks have 

 therefore been lined with rock of different kinds, while in others cement has been 

 combined with gravel and waterworn stones to give the background the appearance 

 of a natural bank. Fresh-water plants, marine algae, sponges, etc., have been used 

 as accessories in these tanks to produce, so far as possible, the appearance of natural 

 conditions. The improvement thus made has been appreciated by the public as well 

 as favorably commented on by persons engaged in aquarium work. 



A large mirror has been installed on the roof of the aquarium and so connected 

 that it throws sunlight at all times of day, through colored glass, into one of the 

 tanks. 



