X PREFACE. 



glands; and in Echidna the young suck off the 

 surface of the skin the secreted milk, for there is no 

 nipple. 



" In the case of certain fish, the ova are hatched 

 in a marsupial sack on the surface of the stomach of 

 the male, and the young, when hatched, feed on the 

 mucus secreted from the skin lining the sack ; 

 and here, as I believe, we see what might be the 

 commencement of a simple mammery gland, as in 

 Echidna, etc. This is, of course, only an hypothesis. 

 The exact steps in the Evolutionary process could be 

 discovered only by the observation of animals which 

 became extinct during the earliest part of the secondary 

 period. 



" Dear Sir, yours faithfully, 



"CHARLES DARWIN." 



We may fairly infer from this letter, 

 that the distinguished founder of what is 

 populary known as " The Darwinian 

 Theory" acknowledged in the maturity 

 of his age and fame first, that it was 

 "only an hypothesis;" and secondly, 

 that the exact steps in the Evolutionary 

 process could only be discovered by the 

 observation of animals which had become 

 extinct ages ago, which seems like admit- 

 ting that it never could or would be 

 proved. 



