110 LECTURES ON EVOLUTION in 



lutional process by which reptiles gave rise to 

 birds. 



The evidential value of the facts I have brought 

 forward in this Lecture mast be neither over nor 

 under estimated. It is not historical proof of the 

 occurrence of the evolution of birds from reptiles, 

 for we have no safe ground for assuming that true 

 birds had not made their appearance at the com- 

 mencement of the Mesozoic epoch. It is, in fact, 

 quite possible that all these more or less avi-form 

 reptiles of the Mesozoic epoch are not terms in 

 the series of progression from birds to reptiles at 

 all, but simply the more or less modified de- 

 scendants of Palaeozoic forms through which 

 that transition was actually effected. 



We are not in a position to say that the known 

 Ornithoscelida are intermediate in the order of their 

 appearance on the earth between reptiles and birds. 

 All that can be said is that, if independent evidence 

 of the actual occurrence of evolution is producible, 

 then these intercalary forms remove every difficulty 

 in the way of understanding what the actual 

 steps of the process, in the case of birds, may have 

 been. 



That intercalary forms should have existed in 

 ancient times is a necessary consequence of the 

 truth of the hypothesis of evolution ; and, hence, 

 the evidence I have laid before you in proof of 

 the existence of such forms, is, so far as it goes, 

 in favour of that hypothesis. 



