The Zoologist — Jdly, 1873. 3585 



them in classification, and the fact of their being almost exclusively 

 found in Australia (only one genus, that of the true Opossums, being 

 found elsewhere, in North and South America), gives us all the 

 more confidence in regarding them as such. At the same time this 

 isolation tells very well in favour of Mr, Darwin's theory. The 

 marsupial is a very early type of mammal, and was at one time 

 much more widely distributed than at present. Prof. Owen figures 

 the lower jaw of a small insect-eating marsupial taken from the 

 Stonesfield oolite in Oxfordshire, England. Now if the placental 

 type, which is a higher and prevailing one, had arisen from one 

 species of marsupials, it would, if the advance was of sufficient 

 importance, have gradually supplanted the lower type, wherever it 

 came into competition with it, and we have only to allow that this 

 struggle did not first occur in Australia, and that all communication 

 with the rest of the world was cut off before the predominating race 

 could reach Australia, and we should expect to find, according to 

 Mr. Darwin, exactly what we do find ; all the animals there re- 

 taining a distinct classification group around the old marsupial 

 type. I wish to make this point very clear and strong, for the 

 clearer and stronger it is the greater the difficulty will be for 

 Mr. Darwin's theory a little further on. 



The sheet-anchor of Darwinism is, that the adaptations of organs 

 to the needs of the animal are not produced by external circum- 

 stances, but that out of the infinite slight variations which arise the 

 one which gives its possessor the advantage in the " struggle for 

 existence" prevails, the less excellent dies out. 



Out of the infinite possibilities for improvement which surround 

 any animal, it would be extremely improbable that the same should 

 be arrived at by different species, and a fortiori when this improve- 

 ment consists of organs exceedingly complicated and apparently 

 difficult of development. 



Let any one consider the wing of a bird, a fly, or a bat, and he 

 will understand what I mean : if we only knew of one organ of 

 flight we might be led to suppose that it was the only mechanical 

 contrivance possible to this end, and yet we see in these instances 

 how entirely distinct are the means to the same action. How 

 rational and in accordance with a priori reasonings it seems to be, 

 that bones should be within the body to support the soft parts and 

 give them by leverage the means of determinate motion ; and yet 

 when we compare invertebrate with vertebrate animals it shows us 



