190 MAMMALIAN DESCENT. [Lect. YIII. 



and to draw out the Flying Cat's skin into a parachute, 

 mthout imagining further and further degrees of the 

 same processes, which, being continued, would inevitably 

 end in the formation of a Bat. If the palaeontologist had 

 not demonstrated these things to us, we should never 

 have conceived of the Pterodactyles, or winged Keptiles, 

 that swarmed in the Secondary epoch ; the contem- 

 poraries, let me remind you, of the Marsupials of our 

 own region. Then, towards the end of that period, the 

 northern hemisphere abounded in Birds quite unlike our 

 horny-beaked, toothless types. These had jaws well 

 furnished with teeth, some of them had teeth standing 

 against the jaw wall (Pleurodont), whilst others had 

 socketed teeth (Thecodont) ; both these methods of tooth- 

 fixture still remain in existing Eeptiles. Further back a 

 little, in the times of the Upper Oolite, Birds existed with 

 a long tail like that of a Lizard, and with the bones 

 of the hand distinct, as in the Lizard, and not melted 

 together, as in the wing of the modern Birds. The flying 

 Lizard (Pterodactyle) shot out one finger into a long, 

 jointed rod, and to this rod the skin forming the wing 

 was attached, like a sail. We are all familiar with the 

 Bat, and a summer evening's walk would lack one of its 

 charms if no Pipistrelle flitted past our face on his moth- 

 hunting raids. But what an excitement there would 

 have been amongst the astonished palaeontologists if 

 the Bats had been all extinct, and just one should have 

 rewarded the labours of a Marsh or a Cope I The Bats 



