PEDIGREES AND FAMILY TIES. 219 



much of the skeleton has been completely but 

 gradually changed in correspondence with the 

 changing habits of the bird. Some of the petrels 

 secrete great quantities of fat, so much so, that 

 the natives of the lonely spots where they breed 

 thread a wick through their dead bodies and 

 burn them like lamps. 



The divers are the expert fishermen of our 

 seas and lochs, as the grebes are of our lakes 

 and broads. Like the diving-petrel, and the auks 

 and guillemots, this group has undergone a great 

 change in the form of the skeleton. The legs 

 have shifted far backwards, and developed 

 special process to give power to the stroke 

 in swimming. The divers have become so 

 highly specialised in this direction that they 

 can no longer walk upon land, but simply push 

 themselves along on their breasts by means 

 of their feet. This similarity in the skeleton 

 of these really very different forms at first led 

 many astray, since they mistook what is really 

 but the result of similar habits and environment 

 for a record of characters acquired by descent 

 from a common ancestor. 



Again we must hasten back to more ancient 

 forms : this time to the vicinity of the game- 

 birds and the crane-tribe. 



These two groups are considered by many of the 

 best authorities to be somewhat nearly related. 



Now the bird of which we are going to speak 

 has long been a puzzle to ornithologists, and con- 

 tinues to be so to this day. It is known as the 

 hoatzin or opisthocomus, and is a native of the 

 Amazon Valley. 



