MARSUPIALIA 301 



law of correlation of animal structures may be successfully 

 applied, and indicates the instances in which — the physio- 

 logical condition being unknown, and the coincident structures 

 being understood empirically — careful observation and rigor- 

 ous comparison must supply the place of the physiologically 

 understood law. 



Those who deny the existence of design in the construction 

 of any part of an organized body, and who protest against the 

 deduction of a purpose from the valves of the veins or the lens 

 of the eye-ball, repudiate the reasoning which the palaeonto- 

 logist carries out from the hoof to the grinder, or from the 

 carnassial molar to the retractile claw, through the guidance 

 of the principle of a pre-ordained mutual adaptation of such 

 parts ; but such minds are not, nor have been, those who 

 have contributed to the real advancement of physiology or 

 palaeontology. 



By reference to the "Table of Strata" (fig. 1), it will be 

 seen that the earliest evidence of a vertebrate animal is of 

 the cold-blooded water-breathing class in the upper Silurian 

 period. Next follows that of a cold-blooded but air-breath- 

 ing vertebrate, under the batrachian grade, in the carbonifer- 

 ous period. The warm-blooded air-breathing classes are first 

 indicated, as birds, by footmarks in a sandstone of probably 

 triassic but not older age ; and, as mammals, by fossil teeth 

 from bone-beds of the upper triassic system in Wirtemberg, 

 and of the same age near Frame, Somersetshire. Mam- 

 malian remains have also been found in a coal-field in North 

 Carolina, which may be earlier, but cannot be later, than the 

 lias formation. 



Genus Microlestes. — The mammalian teeth from German 

 and English trias indicate a very small insectivorous quad- 

 ruped, to which the above generic name was given by Professor 

 Plieninger. The German specimens were discovered in 1847 

 in a bone breccia at Diegerloch, about two miles from Stutt- 



