284 iMr. Percy R. Lowe : 



and has ably interpreted their meaning. In a comparative 

 review of tlie embryology of the common farmyard chick 

 and other members of the game tribe^ he has also indicated 

 some steps in the path along which the descent from the 

 trees to the ground was accomplished. 



From the comparative security of the trees to the many 

 hazards of the gronnd^ whatever may have been the reasons 

 which prompted such a departure, the way has doubtless 

 been mai-ked and punctuated by many intermediate develop- 

 mental adaptations ; but of any of these intermediate stages 

 among present-existing birds we seem to have discovered np 

 to the present time no instances, or, at any rate, we seem to 

 have ignored their existence. 



In the case of the Guans {Ortalis)^ however, I shall hope 

 in this paper to furnish evidence pointing to the conclusion 

 that while the adult Guan lives an almost complete arboreal 

 existence and has young which are hatched in nests amov(j 

 trees and bushes, and that while these young appear to live 

 from almost their earliest days of immaturity the same 

 j)recocious terrestrial existence which is seen in the case of 

 our familiar game-birds, yet that this habit of nesting in 

 trees which the Guan exhibits is vot an instance of a return 

 to ancestral ivays, or, in other words, a case of reversion, 

 but is, on the contrary, an instance among present-existing 

 birds, which nest in trees, of an incompleted movement in 

 the opposite direction — that is to say, towards the purely 

 terrestrial life seen in many of the more modern types of 

 game-birds. 



In his ' History of Birds,' Mr. Pj^craft quotes instances 

 in which precocious young, specially adapted to meet the 

 requirements of a terrestrial nursery, are hatched in trees ; 

 and these instances he regards as examples of rerer^fow to 

 the old ancestral way, among birds, of a purely arboreal 

 life. 



Such examples are supposed to occur in the ease of the 

 Green Sandpiper, the Noddy and the White Tern, and 

 certain species of Ducks. But these instances, I submit, 

 are not comparable to the case of the Guans. 



