No. G24] 



REACTIONS OF PHBYNOSOMA 



37 



water except after the very infrequent heavy rains. Very 

 little water is excreted ordinarily, as when fed on ants, 

 beetles, etc., the feces are eliminated as a dry mass con- 

 taining practically no water, and the urine is composed of 

 an equally dry mass largely made up of crystals of uric 

 acid. When fed on a moist diet, such as grasshopper 

 nymphs from a moist habitat, the feces become softer and 

 are often accompanied by a considerable amount of muci- 

 laginous liquid. The urine, however, remains as usual. 

 The idea that the excretion of waste nitrogen as uric acid 

 is an adaptation on the part of the Reptilia for life in 

 arid regions is well borne out by the conditions in these 

 animals. Urinary analyses made by the writer in the 

 laboratorv of physiological chemistry of the University 

 of Illinois give the following results (1917^) : 



Urea nitrogen 0.0 



Uric acid 765.0 



Uric acid nitrogen 255.0 



Phosphorus as P,0, 3.5 



It will be observed that uric acid accounts for prac- 

 tically all of the nitrogen contained in the urine and that 

 urea is entirely absent. In this respect the urine of the 

 horned lizard differs from that of the aquatic and semi- 

 aquatic reptiles, which contains a consideral)le amount of 

 urea, as does that of birds, another group in wliich the 

 uric acid content is high. 



5. Rcproduefioii. — It is in connection with Pliri/uosoma 

 cornnfum tliat the long-disputed question as to the vivi- 

 l)arity of (»\ i]»arity of the members of this genus may be 

 opoiuMl a-ain. (\)]ie (1898) states that Phrynosoma is 

 ovi]>ar()us. wliich is denied by Ditmars (1908) and Watson 

 (1911), the latter of whom bases his statement on obser- 

 vations of P. flonglassn. On July 5, 1917, some twenty 

 specimens of P. conmtum were received at the vivarium 



