THE YOUNG NATURALIST. 



development took place on various lines. Some of its progeny possessing 

 longer hind-legs and shorter fore-legs, assumed occasionally an erect 

 attitude. These peculiarities proving advantageous were more marked 

 in their successors, whose skeletons became more bird-like, till some, 

 as Compsognathus, possessed a swan-like neck, a small bird-like head, and 

 habitually assumed an erect position, with the fore-legs free, and were 

 aided in balancing by the tail, which dragged along the ground. Some of 

 these silvan Saurians, jumping from bough to bough, with outspread limbs, 

 would naturally become possessed of a membranous support, as in the so- 

 called flying squirrels. Of all the descendants of this primitive reptile, none 

 are more remarkable than the Pterosauria, an order of flying lizards present- 

 ing some bird-like peculiarities of structure. This order, which includes the 

 Pterodactyles, must be regarded as a reptilian development in the direction 

 of flight, and not as the direct ancestors of birds which had already been 

 evolved on more advantageous lines. Thus we see, then as now, the per- 

 sistent and inscrutable law of variation silently working in all directions. 



Having foreshadowed the perfect bird in its reptilian ancestors, and bear- 

 ing in mind that even the wings, often regarded as exclusively avian struc- 

 tures, were possessed by many fossil reptiles, the only apparent distinction 

 left to us, is, that birds possess feathers, which are an epidermic exo-skeleton 

 and strictly homologous to the scales of reptiles. It will thus be seen that the 

 boundary line between reptiles and birds is really non-existent from an evolu- 

 tionary point of view, as feathers are simply a further development of scales. 

 The more geology is studied, the more difficult does it become to find a defi- 

 nite dividing line between reptiles and birds ; in this, as in other branches of 

 science, classification is to a great extent arbitrary — order melting into order, 

 and kingdom into kingdom, the more carefully they are studied; till we see 

 from the lowliest plant to man himself, one harmonious whole, which by the 

 operation of those laws, silently working now as they have been through un- 

 told aeons, have produced from the simplest protoplasmic cell, the widely 

 difFering forms of life which now surround us. Assuming then, that feathers 

 are the distinguishing character between reptiles and birds, we find in Arch- 

 seopteryx the first feathered reptile or reptilian bird. The Archasoptergidae 

 were undoubtedly contemporaneous with, and in fact earlier than some species 

 of Pterosaurians ; the earliest Archseopteryx occurring early in the Jurassic 

 period, while the largest Pterosaurians occurred about the middle of the 

 Cretaceous period. These fossil birds differed from any of the existing 

 species in the possession of teeth, and in the absence of the coccygean bone. 

 The tail of Archseopteryx is reptilian in character, consisting of a number 

 (20) of elongated vertebras, each supporting a pair of quill feathers. Although 



