that connect the Orders and Families of Birds. 469 



Among the advantages derived from an inspection of the fore- 

 going diagram is that of our being able to discern at one view the 

 gradual deviation which takes place in the various groups from 

 the more typical form and character of the order. If we fix our 

 attention steadily on the central and typical group of Conirostres, 

 we may trace out at a glance the limits by which that perfect for- 

 mation depending upon the more important characters is partially 

 preserved, or entirely lost, according as the groups we examine 

 are more or less in its vicinity. Let us select, for instance, such 

 essential characters as strength and regular construction of the 

 bill and foot, the powers of the voice, or the organs of digestion. 

 We see the first of these characters, the perfect bill of the Coniros- 

 tres, preserved in the neighbouring Scansores, though partially 

 superseded by the use of the tongue in the Picidce and Certhiadce, 

 until it is entirely lost in the Tenuirostres, and the typical fami- 

 lies of the Fissirosfres. We see it again recovered in those aber- 

 rant families of that tribe which join the Dentirostres, where the 

 perfect form re-appears, though the strength is not equal to that 

 found in the typical tribe of the order. The perfect foot again 

 may be perceived to become in some measure defective in the 

 Scansores, to be entirely lost in the types of the Tenuirostres and 

 Fissirostres, and finally to be resumed as we come round by the 

 Dentirostres to the tribe from which we set out. We may again 

 mark out, on examining this diagram, how far the more perfect 

 powers of voice that distinguish the typical groups of the Coniros- 

 tres, are communicated to the neighbouring families on each side ; 

 such as the Psittacida among the Scansores, the Merulidce and Syl- 

 viadcB among the Dentirostres ; but how completely they are lost in 

 the remoter families. The same observation may be made re- 

 specting the more extensive powers of digestion which distinguish 

 the omnivorous families of the same typical tribe. These powers 

 are perceived to be singularly deficient in the remote groups of 



3 p 2 the 



