"248 CERTAIN CRITERION/ [CHAP. n. 



of distinguishing the species of this genus, similar to 

 that which has been so successfully applied by our dis- 

 tinguished countryman Yarrell to the Swans ; namely, 

 by observing the very remarkable windings of the wind- 

 pipe in each. A reference to this criterion, when pos- 

 sible, is found to relieve the bewildered naturalist from 

 uncertainties into which the little dissimilarity of the 

 outward appearances betray him.* In the Penelopes, 

 the windpipe, before entering the cavity of the body 

 and communicating with the lungs, makes various cir- 

 cuits on the surface of the muscular part of the breast, 

 between the skin and the flesh. These circuits are 

 constantly formed on the same plan in the same species, 

 as far as opportunities have yet occurred of observing 

 their comparative anatomy ; and it is very curious, on 

 skinning a bird, to find the windpipe meandering on 

 the outside of the flesh, looking almost as if the internal 

 organs had been protruded or ruptured by accidental 

 violence. But so far from this being a defect or an in- 

 firmity, we find that some of the arrangements and 

 contrivances, by means of ligaments, tissue, &c., to pre- 

 vent any displacement of the windwipe from its intended 

 position (for instance, those in the Penelope marail, and 

 in the Penelope parr akoua], are beautiful examples of 

 design, and are worthy of quotation in any future work 

 on Natural Theology. The consequence of this long 

 and externally- winding trachea is a voice of great variety 



* "J'invite les naturalistes, a ne point decider trop legerement 

 sur 1'apparent identite des especes, qui composent le genre Penelope ; 

 je m'y suis souvent abuse, avant d'avoir bien saisi les caracteres qui 

 distinguent ces especes, dont le plumage n'offre que peu ou point de 

 dissemblance; et chez lesquelles, les caracteres qui tiennent aux 

 formes enterieures, sont tres-peu apparents." Temminck. 



