136 Journal of the Mitchell Society [3Iarch 



under a projecting ledge of rock. While it may be unwarranted to 

 state as a general principle, all nests that I have observed faced the 

 east. 



The burrow excavated to such depth that the female is about hid- 

 den from view, she lays therein the cream-white, leathery-skinned 

 eggs. The eggs are elliptical in form and measure 15 mm. in 

 length by 10 to 11 mm. in diameter. They are dropped into the 

 burrow one at a time. Each egg is covered over with a thin layer 

 of dirt, scraped down by the hind legs of the mother, before the next 

 egg is laid. Finally, the eggs all laid, the female packs the nest with 

 the remaining dirt, smoothes it off and scurries away. After a day 

 or two, the site is indistinguishable. 



So far as known to the writer egg-laying may occur, in Kansas, 

 anywhere between the end of May and sometime late in July. I have 

 no facts to offer regarding the duration of the incubation period which 

 Strecker states to be from 35 to 40 days in Texas, except that it must 

 vary with the stage reached at laying and the temperature. 



During this entire study no aspect was more interesting than that 

 of the mutual fitness of the developing eggs in their envelopes with that 

 of their earth-nest environment, which serves as a temperature and 

 moisture-controlling brood-pouch. Through some inherited complex 

 of instincts the female selects a site combining the advantage of drain- 

 age, rooting, exposure to heating b}^ the sun, and ventilation. Under 

 certain conditions they become turgid and swell, but shrivel like a 

 raisin when allowed to dry. When the latter occurs the eggs are 

 vulnerable to the attacks of ants, the mandibles of the insects cutting 

 through the folds of the shell. When the shell is turgid and smooth 

 the ants can do nothing of the kind. 



Daily observing the creatures in their environment the realization 

 is born in upon one that they are literally autochthones, born of the 

 careful regulation of conditions in which they have evolved. 



development of characteristic external features 

 OF the embryo 

 In so brief an account but little may be said upon this subject 

 except to state that the early stages, as shown by the figures here 

 demonstrated, are characteristically reptilian. About stage 32, how- 

 ever, phrynosoman characters put in their appearance, the rosettes 

 of large dorsal scales being heralded by single rounded protuberances. 



