211 Professor Owen, [April 12, 



fertility of monstrous offspring ; on the possibility, e.g., of a variety of 

 auk being occasionally hatched with a somewhat longer winglet, and 

 a dwarfed stature ; on the probability of such a variety better adapting 

 itself to the changing climate or other conditions than the old type — 

 of such an origin of Alca tordu, e.g. ; — but to what purpose ? Past 

 experience of the chance aims of human fancy, unchecked and un- 

 guided by observed facts, shows how widely they have ever glanced 

 away from the gold centre of truth. 



Upon the sum of the evidence, which, in the present course I have 

 had the honour to submit to you, I have affirmed that the successive 

 extinction of Amphitheria, Spalacotheria, Triconodons, and other 

 mesozoic forms of mammals, has been followed by the introduction 

 of much more numerous, varied, and higher-organised forms of the 

 class, during the tertiary periods. 



There are, however, geologists who maintain that this is an 

 assumption, based upon a partial knowledge of the facts. Mere 

 negative evidence, they allege, can never satisfactorily establish the 

 proposition that the mammalian class is of late introduction, nor prevent 

 the conjecture that it may have been as richly represented in secondary 

 as in tertiary times, could we but get evidence of the terrestrial fauna 

 of the oolitic continent. To this objection I have to reply : in the 

 palaeozoic strata, which, from their extent and depth, indicate, in the 

 earth's existence as a seat of organic life, a period as prolonged as 

 that which has followed their deposition, no trace of mammals has 

 been observed. It may be conceded that, were mammals peculiar to 

 dry land, such negative evidence would weigh little in producing 

 conviction of their non-existence during the Silurian and Devonian 

 aeons, because the explored parts of such strata have been deposited 

 from an ocean, and the chance of finding a terrestrial and air-breathing 

 creature's remains in oceanic deposits is very remote. But, in the 

 present state of the warm-blooded, air-breathing, viviparous class, 

 no genera and species are represented by such numerous and widely 

 dispersed individuals, as those of the order Cetacea, which, under the 

 guise of fishes, dwell, and can only live, in the ocean. 



In all cetacea the skeleton is well ossified, and the vertebrae are 

 very numerous : the smallest cetaceans would be deemed large 

 amongst land mammals ; the largest surpass in bulk any creatures 

 of which we have yet gained cognizance : the hugest ichthyosaur, 

 iguanodon, megalosaur, mammoth, or megathere is a dwarf in com- 

 parison with the modern whale of a hundred feet in length. 



During the period in which we have proof that Cetacea have 

 existed, the evidence in the shape of bones and teeth, which latter 

 enduring characteristics in most of the species are peculiar for their 

 great number in the same individual, must have been abundantly 

 deposited at the bottom of the sea ; and as cachalots, grampuses, dolphins, 

 and porpoises are seen gambolling in shoals in deep oceans, far from 

 land, their remains will form the most characteristic evidences of 

 vertebrate life in the strata now in course of formation at the bottom 

 of such oceans. Accordingly, it consists with the known characteris- 



