438 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1907. 
The roof is of glass bricks, of the Falconnier system, with the ex- 
ception of a ventilating roof that runs the whole length of the hall, 
so that the cages are much better lighted than the hall. The advan- 
tage of these glass bricks, which also cover the exterior cages, is that 
they aré an excellent protection against too sudden cooling and 
against currents of air, while they let the ight pass freely. They are 
hollow and the interior cavity, because of the high temperature at 
which they are molded (850°) presents an almost absolute vacuum. 
This system advantageously replaces that of double windows. A 
shallow groove around each brick makes it possible to lay it in a cer- 
tain amount of cement, so that the system is united in a very solid 
manner. The large windows at either end of the hall and the mov- 
able frames of the ventilation roof are fitted with ordinary window 
glass. 
There are 37 interior and 11 exterior cages for the monkeys; some 
of them are 6 meters in diameter; almost all the others have a super- 
ficial area of 4 square meters; they are protected from the public by 
an iron balustrade which supports a grillage 2 meters in height. The 
floor of the cages, raised 0.75 meter above that of the hall, is formed 
of a thin layer of concrete, and supports a tree upon which the 
animals may climb, the trunk of which is carefully set in a cast-iron 
tube. The walls are lined with ivory-white glazed bricks; all the 
corners are rounded. The side of the cage presented to the public 
is closed by a grillage whose meshes do not correspond with those 
of the exterior grillage, so that it is very difficult to throw bread or 
anything else to the animals; only the cages of the anthropoids are 
provided with vertical bars. 
The back wall of each cage has at its upper part a recess lighted 
by a window which looks out above a service passage, and in this 
upper part there is, in the cages of the south side only, the passage 
by which the monkeys reach the exterior cages. At one end of this 
passage is a movable trapdoor that the monkeys can easily raise, 
at the other a sliding door that the keepers can shut or open from 
the service passage by means of a chain. 
All the cages havea glazed interior roof set obliquely from the front 
backward, attached on one side to the common roof, on the other 
supported by the grill in front. Each cage communicates with the 
service passage (1 meter wide, 2 meters high) by a vertical panel, 
and in this panel is an opening for introducing food and a small 
window that lights the passage and permits an inspection of the 
cage. In the service passage there are a certain number of cocks 
for drinking water, hot water, and gas, and a gutter to take off the 
drip from washing the cages. From the southern passage similar 
access may be had to the exterior cages. 
The system for heating and ventilating this house appeared to me 
particularly well conceived. I visited it in the morning accompa- 
