24 THE YOUNG NATURALIST. 



snake possesses either a sternum or anterior extremities; and in the excep- 

 tional cases mentioned both pelvis and legs are rudimentary. This theory 

 is strongly supported by the fact that no traces of ophidian remains have 

 been found earlier than the older Tertiary, strata. Nevertheless it must not 

 be imagined that snakes are less perfectly fitted to sustain the struggle for 

 existence than their compeers. The majority of snakes possess poison fangs, 

 varying in complexity of structure, from the moveable maxillary tooth of the 

 Viperine snakes, with its complete perforation, to the open grooved fixed 

 fang of the poisonous Colubers, which also are homologous to the fangs of 

 the poisonous lizards. 1 he venom which gives these otherwise feeble creatures 

 their deadly power, is merely an exceptional development of one of the elements 

 of the saliva of the other vertebrates. It is only in the smaller snakes that 

 this development takes place, the larger ones are able to carry on successfully 

 the struggle for existence by means of their great constricting powers. 



Again, we find snakes adopting themselves to marine life, and their tails 

 developing an eel-like form ; they are all comparatively small, and hence we 

 find that all have acquired the poison apparatus, without which they would 

 have been unable to maintain the battle of life. Though with the exception 

 of one lizard these are the only existing marine reptiles, yet in the Second- 

 ary period, the seas were tyrannized over by gigantic lizards, such as the 

 Plesiosaurus and the Ichthyosaurus, adaptations of reptilian type to marine 

 life. Contemporary with these we find the Dinosaurians, an order which in- 

 cluded the herbivorous Hylseosaurus and Iguanodon, and the carnivorous 

 Megalosaurus. Some of these giants attained a length of 60 or 70 feet, and 

 present most curious, and in fact almost incredible modifications of structure. 

 The Iguanodon, with a body about 25 ft. long, habitually assumed an 

 erect attitude. It is difficult to picture to ourselves the appearance of a 

 creature, much heavier than a hippopotamus and longer than a crocodile, sit- 

 ting and moving in kangaroo fashion. That such creatures have existed 

 there is no doubt, for we find their remains, and can from them build up 

 their skeletons, as certainly as those of existing reptiles, It may be asked — 

 Why did these giants fail to keep their place, despite their power and size ? 

 There is only one answer to this question, viz., inability to find food, owing 

 primarily to altered climatic conditions. 



The most bird-like in structure of all fossil reptiles is the remarkable 

 Compsognathus longipes, which undoubtedly presents a close approximation, 

 if not an absolute resemblance, to the first flying reptile from which the birds 

 were evolved. It would be extravagant to suppose that a reptile ever directly 

 produced a bird, but it is obvious that all existing reptiles and birds are des- 

 cended from a common reptilian ancestor. From this primitive Sauropsidan, 



