Ee 
11 
He proposed to call attention to that unity of plan which we 
so constantly found persisting through extreme diversity of 
detail and confessed that the only explanation of this persistence 
which satisfied his own mind was Heredity. 
Taking as his starting point the period when the coal was 
forming, and the only occupants of the dryer portions of the globe 
appeared to have been amphibia, attention was drawn to the 
remains of Archegosaurus, one of the larger and more heavily 
armoured species. Though nota lizard, as we now understand the 
term, and differing from all subsequent true lizards in the forma- 
tion of the spinal column, yet this highly specialised amphibian, 
was in itself so unmistakably crocodilian and was connected with 
the true crocodiles of later epochs by so many intermediate forms 
in successive deposits, that it seemed likely that we had in it the 
link between the Amphibia and the Reptilia. 
At some point of this chain of development the Archosauria 
(First or Harly Lizards) appeared, bulky animals of the crocodile 
type for the most part, one branch of whose descendants continuing 
aquatic and varying but little became in time Crocodiles, whilst 
other branches changing their habitat and habits and varying 
much became either aerial as the Pterodactyls, marine as the 
Ichthyosauria or fitted for a life on dry land as were many of the 
Dinosauria. 
Aétosaurus and Phytosaurus of the German Trias which 
seemed to have been long-limbed terrestrial lizards, probably 
vegetarian in diet but of crocodilian appearance, in some way 
connected the Archosauria to the more highly specialized 
Scelidosaurus of secondary times. This animal recalled the 
Fleet Street Griffin shorn of his wings, he was almost un- 
armoured, the ancestral plate mail having disappeared from back 
and breast but lingering in a series of lateral scutes suggestive 
of the ports of a man-o’-war. ‘The most noticeable change was 
the mode of progression, this branch of the great lizard stock 
was biped, the fore limbs small and unimportant, the hind limbs 
long and powerful forming with the tail a tripod upon which the 
elvis (now becoming important and bird-like in form) and the 
ower spine (now found auchylosed into a stiff rod as in birds) 
were upheld in an almost erect position. ‘I'his animal probably 
browsed upon the foliage of low trees. Another change had 
taken place, the functional toes of the hind foot were reduced to 
four and in the next form to which the lecturer called attention, 
the Iguanodon of the Wealden Deposits, these digits were but 
three and the form of the foot had become unmistakably avian, 
