I89I.] 



THE BRITISH NATURALIST. 



123 



Before leaving this part of our subject, it may be well to note the 

 parallelism between the sloughing of reptiles and the moulting of 

 birds. All reptiles cast their skins periodically, and the same holds 

 good of the moult of birds. If part of a scale of a reptile be 

 cut off it will not be replaced till after sloughing ; in the same way, if 

 a feather be cut partly away, it will not grow nor be renewed till the 

 next moult, for it is known that after a feather has grown to its full 

 size it receives little or no further nourishment. When the moulting 

 season arrives, the old feathers are pushed off and speedily replaced by 

 new ones which rapidly attain their full size ; the process of moulting is 

 not quite so rapid as the sloughing of a reptile, but, like it, is accom- 

 panied by considerable disturbance of the animal's system, so much 

 so that birds die during the moult as reptiles do during the slough. 



Referring again to that solitary species ArchcBopteryx macmra which 

 is of such cardinal importance in the eyes of the evolutionist, though, 

 no doubt millions of other closely allied forms lived but have left no 

 trace, for it must be remembered that the small size and slight bones 

 of these birds make it certain that few would be preserved in a fossil 

 state, the most striking part of its skeleton is the tail which gives it 

 its specific name. 



Archcsopteryx macrum possessed a tail more lizard-like than that of 

 any other known bird, recent or fossil, consisting as it did of 20 

 elongated vertebrae each supporting a long feather on either side. 

 It will be evident that this long slender tail would be almost useless 

 as a rudder during flight, and if the bird alighted on the ground it 

 would be liable to injury, and might be a source of danger to its 

 possessor, the feet of Archceopteyx however tell us distinctly, that it 

 was a perching and tree-loving bird. The two fossils of this species 

 are the first and last, so far as we know, characterised by this form of 

 tail, all subsequent bird-fossils possess a coccygean bone, which is 

 formed by the coalescence of several of the last caudal vertebrae. 

 This form of tail contrasts in a marked manner with the earlier 

 reptilian one ; and has superseded it because of the more effective 

 rudder of which it is the support. The fan-like arrangement of the 

 tail feathers, characteristic of all existing flying birds, is only possible 

 where this coccygean or ploughshare bone has been developed ; and 

 just as in the Oolite period flying birds had been developed under the 

 circumstances already described, so the further development of the 



