292 Mr. Percy R. Lowe : 



never been conditions in its surroundings potent enough to 

 make a descent to the ground a permanent necessity. 



It is interesting to note, however, that in Texas, the most 

 northerly limits of the Guan's distribution, and where the 

 conditions are very much drier and consequently the vege- 

 tation infinitely more scanty, "the birds are said to nest in 

 the heaps of leaves accumulated under the Mesquite-bushes " 

 {cf. Boucard, P. Z. S. 1883, p. 460). If this is true, it 

 seems to illustrate a further step in the descent to the 

 ground, induced by altered conditions of environment. 



The fact that the young, as we shall later see, live upon 

 the ground, while the adults spend their existence in the 

 trees, seems to point to the fact that the Guan has either 

 failed to completely adapt itself to one or the other environ- 

 ment, or that there has never arisen the necessity to do so. 



In a most interesting account of the habits of the Hoatzin, 

 Mr. Beebe, in 'Our Search for a Wilderness/ remarks: — 

 " Inexplicable though it may appear, the Hoatzin — although 

 evidently unchanged in many respects through long epochs — 

 yet is far from being perfectly adapted to its present environ- 

 ment. It has a severe struggle for existence, and the least 

 increase of any foe or obstacle would result in its extinction.^' 



Indeed, except that the Guan has apparently made one step 

 downwards to the ground, it reminds us forcibly, in point of 

 diet, habits, and ways generally, of the Hoatzin, which is 

 essentially a primitive type of bird addicted to an almost 

 complete arboreal existence (cf. J. J. Quelch, ' Ibis,' 1890, 

 p. 327). 



Some structural features of the Guan. 



To some it may appear venturesome thus to compare the 

 Guan and the Hoatzin ; but in many respects the latter bird 

 presents structural features distinctly pointing to its affinities 

 with the Gallinae, and perhaps in none more so than in its 

 well-differentiated csecal colon; for it will be remembered 

 that the ileo-colic region reaches its highest state of speciali- 

 zation in birds which live mainly on a purely vegetable diet. 



Dr. E. A. Wilson, for instance, has drawn attention, 

 in "The Grouse in Health and Disease" (Report of the 



