in my opinion, been somewhat underestimated. This is the Uro- 

 pygi or whip-tailed scoiTJion. The whip-tails are armed with 

 a pair of grapples rather than pincers, and have piercing mouth 

 parts. They hook onto their prey and squeeze it to their mouths 

 so that these protruding devices may puncture its hide. Most 

 Uropygi are small, but there are some in this province that are 

 three inches long. They inject a fluid that, if it gets under the 

 skin, produces excruciating burning sensations and inflamma- 

 tion. They are rare creatures, but no case is, as far as I know, on 

 record of death from them. 



INTO THE BOLSONES 



If we cross the Rio Grande gorge and travel into upper Mexico 

 we find ourselves in a vast desierto that extends across the state 

 of Chihuahua and is traversed by only one north-to-south road. 

 Here we are in the center of the Desert Belt although at an 

 altitude of some three to four thousand feet. The country is very 



arid, and as true a desert as any on this continent, yet most of 

 it is clothed in quite profuse plant life. The cactus flora is some- 

 what different from that of Sonora, but the creosote bush again 

 holds sway along with saltbush, some scrub huisache, and a 

 great many yuccas. As a whole, the cactuses, yuccas, and the 

 creosote bushes here grow below the 3500-foot level and grease- 

 wood and sages above these and up to about 5000 feet. Above 

 this comes grass — the montane zone of the subtropical savan- 

 nahs — and very soon appear small isolated cedars and junipers, 

 which coalesce upward and in turn give way to pines and firs 

 above 7000 feet. The true northern or boreal coniferous zone is 

 represented on the very tops of the mountains at over 8500 feet. 

 The plateau is a vast level plain with ridge after ridge of 

 mountains running from northwest to southeast. These rise on 

 an average about 3500 feet above the level floor. In between are 

 shallow bowls called by the Spanish bolsones, which are shallow 

 lakes after rain but dry dust bowls during the rest of the year. 

 The present topography was formed by extensive faulting, blocks 

 or rather long strips of territory rising up to form the mountain 



Trap-door Spiders are found all over the ivorld but their wonderfully constructed hinged door- 

 :-!'\'\ are particularly noticeable en fhi:: i!f<rrt 



^^i^" 



