REACTIONS OF THE HORNED LIZARD. IOI 



3. Behavior in Captivity. 



In captivity they are rather inactive, except when living food 

 animals are introduced into the cage, when they may become very 

 active, or when otherwise disturbed. They spend a great deal of 

 time with the belly flattened to the ground, with the head lowered 

 and the eyes closed. When the sun is not shining directly on the 

 cage the majority of the animals are oriented toward the source 

 of light (e. g., a window) and often climb up on the side of the 

 cage toward the light. On a cool morning they often orient 

 themselves with respect to the sun so that the surface of the back 

 is as nearly as possible perpendicular to the path of the rays. 

 This is accomplished by tilting the body sidewise. When the air 

 temperature is in the neighborhood of 30 or above direct sunlight 

 is avoided, and the animals are active only when the cage is shaded. 

 This is not in line with reported field observations on Phryno- 

 soma, most of which seem to be based on the true desert species. 



The horned lizards used for the following experiments were 

 taken near the lower edge of the "mesa" (altitude 1,700 m.) 

 just east of the city of Albuquerque, New Mexico, and near the 

 campus of the University of New Mexico, about June 10, and 

 shipped by express to the University of Illinois. They were kept, 

 during the experiments, in two lots, one (cage No. i) in a cage 

 on the floor of a northeast second-floor room of the vivarium 

 building, where, the sunlight reached the cage but a few hours 

 each forenoon. The evaporation in this cage, as measured with 

 the Livingston porous cup atmometer averaged .5 c.c. per hour 

 or 12 c.c. in 24 hours. The other lot was kept in a similar cage 

 in the ground-floor greenhouse, where they were subjected to the 

 direct rays of the sun until 2 P.M. The evaporation was here 

 .8 c.c. per hour. The animals were fed black ants the greater 

 part of the time, with occasional feedings of miscellaneous insects 

 from net sweepings of vegetation near the building. 



II. EXPERIMENTAL RESULTS. 



i. Air Humidity Gradients. (Evaporation Varied by Differences 



in Air Humidity.) 



A large number of experiments (120) were performed with the 

 object of determining the optimum air evaporation and the 



